Fix warning with ipython 8.11 (was #35235)

[tornaria]

📚 Description

ipython 8.11 throws new warnings "UserWarning: Shell was already running a gui event loop for sage; switching to sage." when running some tests.

This is because sage indeed tries to install the same gui event loop for ipython again and again. The fix is checking if the ipython input hook is already set to the sage input hook, in that case we don't install the gui event loop again.

In the test, we run install() twice so we can verify that running it multiple times won't cause a warning anymore.

📝 Checklist

• I have made sure that the title is self-explanatory and the description concisely explains the PR.
• I have linked an issue or discussion.
• I have created tests covering the changes.

⌛ Dependencies

Replaces: #35235

Since gh doesn't allow to change the branch on a PR.

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: e9c3333

[kiwifb]

Already discussed before, and the corrections I suggested did allow the doc to build.

[antonio-rojas]

With ipython 8.12 there seem to be more changes that cause more tests to fail:

**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/attach.py", line 577, in sage.repl.attach.reload_attached_files_if_modified
Failed example:
    shell.run_cell('attach({0})'.format(repr(tmp)))
Expected nothing
Got:
    Installed sage event loop hook.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/attach.py", line 588, in sage.repl.attach.reload_attached_files_if_modified
Failed example:
    shell.run_cell('reload_attached_files_if_modified()')
Expected:
    ### reloading attached file tmp_....py modified at ... ###
Got:
    ### reloading attached file tmp_r6sjhvps.py modified at 20:38:38 ###
    Shell is already running a gui event loop for sage. Call with no arguments to disable the current loop.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/attach.py", line 593, in sage.repl.attach.reload_attached_files_if_modified
Failed example:
    shell.run_cell('detach({0})'.format(repr(tmp)))
Expected nothing
Got:
    GUI event loop hook disabled.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/ipython_extension.py", line 140, in sage.repl.ipython_extension.SageMagics.attach
Failed example:
    shell.run_cell('%attach ' + f.name)
Expected nothing
Got:
    Installed sage event loop hook.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/ipython_extension.py", line 150, in sage.repl.ipython_extension.SageMagics.attach
Failed example:
    shell.run_cell('reload_attached_files_if_modified()')
Expected:
    ### reloading attached file ... modified at ... ###
Got:
    ### reloading attached file tmpfm2j96tr.py modified at 20:41:15 ###
    Shell is already running a gui event loop for sage. Call with no arguments to disable the current loop.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/ipython_extension.py", line 155, in sage.repl.ipython_extension.SageMagics.attach
Failed example:
    shell.run_cell('detach(%r)' % f.name)
Expected nothing
Got:
    GUI event loop hook disabled.
**********************************************************************

[tornaria]

With ipython 8.12 there seem to be more changes that cause more tests to fail:

**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/attach.py", line 577, in sage.repl.attach.reload_attached_files_if_modified
Failed example:
    shell.run_cell('attach({0})'.format(repr(tmp)))
Expected nothing
Got:
    Installed sage event loop hook.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/attach.py", line 588, in sage.repl.attach.reload_attached_files_if_modified
Failed example:
    shell.run_cell('reload_attached_files_if_modified()')
Expected:
    ### reloading attached file tmp_....py modified at ... ###
Got:
    ### reloading attached file tmp_r6sjhvps.py modified at 20:38:38 ###
    Shell is already running a gui event loop for sage. Call with no arguments to disable the current loop.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/attach.py", line 593, in sage.repl.attach.reload_attached_files_if_modified
Failed example:
    shell.run_cell('detach({0})'.format(repr(tmp)))
Expected nothing
Got:
    GUI event loop hook disabled.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/ipython_extension.py", line 140, in sage.repl.ipython_extension.SageMagics.attach
Failed example:
    shell.run_cell('%attach ' + f.name)
Expected nothing
Got:
    Installed sage event loop hook.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/ipython_extension.py", line 150, in sage.repl.ipython_extension.SageMagics.attach
Failed example:
    shell.run_cell('reload_attached_files_if_modified()')
Expected:
    ### reloading attached file ... modified at ... ###
Got:
    ### reloading attached file tmpfm2j96tr.py modified at 20:41:15 ###
    Shell is already running a gui event loop for sage. Call with no arguments to disable the current loop.
**********************************************************************
File "/usr/lib/python3.10/site-packages/sage/repl/ipython_extension.py", line 155, in sage.repl.ipython_extension.SageMagics.attach
Failed example:
    shell.run_cell('detach(%r)' % f.name)
Expected nothing
Got:
    GUI event loop hook disabled.
**********************************************************************

I noticed these and I was wondering what to do about it. I don't see a way to avoid the messages Installed sage event loop hook. and GUI event loop hook disabled. since they are hardcoded in ipython with no way to silence them.

OTOH, the message Shell is already running a gui event loop for sage. Call with no arguments to disable the current loop. is not shown at all when this PR is applied, since we no longer reinstall the event loop.

Note that Volker is already merging this PR in his tree, so I'll keep it as is and open a new PR for ipython 8.12.