fix: Regression of session create-from-template command

[jopemachine]

Follow-up of #1838.

Steps to reproduce the issue

1. Create session template using example-session-templates.yaml

./backend.ai sesstpl create -f ./fixtures/manager/example-session-templates.yaml

2. Try to create a session using the created template.

./backend.ai session create-from-template <session_template_id>

Then the following error is displayed.

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/jopemachine/backend.ai/src/ai/backend/cli/__main__.py", line 10, in <module>
    main(max_content_width=shutil.get_terminal_size().columns - 2)
  File "/home/jopemachine/backend.ai/dist/export/python/virtualenvs/python-default/3.12.4/lib/python3.12/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jopemachine/backend.ai/src/ai/backend/cli/extensions.py", line 25, in main
    super().main(
  File "/home/jopemachine/backend.ai/dist/export/python/virtualenvs/python-default/3.12.4/lib/python3.12/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/home/jopemachine/backend.ai/dist/export/python/virtualenvs/python-default/3.12.4/lib/python3.12/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jopemachine/backend.ai/dist/export/python/virtualenvs/python-default/3.12.4/lib/python3.12/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jopemachine/backend.ai/dist/export/python/virtualenvs/python-default/3.12.4/lib/python3.12/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jopemachine/backend.ai/dist/export/python/virtualenvs/python-default/3.12.4/lib/python3.12/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jopemachine/backend.ai/src/ai/backend/client/cli/session/lifecycle.py", line 442, in create_from_template
    prepared_mount, prepared_mount_map, _ = (
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: not enough values to unpack (expected 3, got 2)

---

Checklist: (if applicable)

• Milestone metadata specifying the target backport version

[jopemachine]

• fix: Regression of session create-from-template command #2761 👈
• main

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