Fix doctests with ipython 8.12

[tornaria]

📚 Description

As reported in #35337 (comment), the update to ipython 8.12 introduces some useless output when calling get_ipython().enable_gui(...) which causes a few doctest failures.

This PR silences this output by (temporarily) redirecting stdout to a string.

This is only one commit that sits right on top of e9c3333 from #35337.

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• Existing tests already cover the changes.

⌛ Dependencies

• Fix warning with ipython 8.11 (was #35235) #35337

[tornaria]

I don't undestand the check failures. They are certainly unrelated to this PR. What confuses me is that #35337 had all checks passed and this PR has just one small commit on top.

[tornaria]

I merged with develop (10.0.beta7) and get the same failures, so I'm undoing the (useless) merge.

[kiwifb]

I agree the failures are unrelated to this. As far as I understand things. I will switch to ipython 8.12.0 sometimes today to look at this properly.

[kiwifb]

Checked it works with both ipython 8.11 and 8.12 without problems.