Check sagemath kernel integrity robustly

[kwankyu]

Fix a bug discussed in https://groups.google.com/g/sage-devel/c/rxfhmspCeuw

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit c157057; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[kwankyu]

Thanks!

[vbraun]

I'm getting

File "src/sage/repl/ipython_kernel/install.py", line 253, in sage.repl.ipython_kernel.install.SageKernelSpec.check
Failed example:
    SageKernelSpec.check()  # random
Exception raised:
    Traceback (most recent call last):
      File "/Users/buildbot-sage/worker/sage_git/build/src/sage/doctest/forker.py", line 734, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/Users/buildbot-sage/worker/sage_git/build/src/sage/doctest/forker.py", line 1158, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.repl.ipython_kernel.install.SageKernelSpec.check[1]>", line 1, in <module>
        SageKernelSpec.check()  # random
        ^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/buildbot-sage/worker/sage_git/build/src/sage/repl/ipython_kernel/install.py", line 267, in check
        if Path(shutil.which(spec.argv[0])).resolve() != Path(sys.executable).resolve():
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/buildbot-sage/worker/sage_git/build/local/var/lib/sage/venv-python3.12.5/lib/python3.12/pathlib.py", line 1162, in __init__
        super().__init__(*args)
      File "/Users/buildbot-sage/worker/sage_git/build/local/var/lib/sage/venv-python3.12.5/lib/python3.12/pathlib.py", line 373, in __init__
        raise TypeError(
    TypeError: argument should be a str or an os.PathLike object where __fspath__ returns a str, not 'NoneType'

on some platforms, e.g. http://build.sagemath.org/#/builders/68/builds/6

[kwankyu]

The patch will deal with the NoneType case.

[vbraun]

Now getting

**********************************************************************
File "src/sage/repl/ipython_kernel/install.py", line 253, in sage.repl.ipython_kernel.install.SageKernelSpec.check
Failed example:
    SageKernelSpec.check()  # random
Exception raised:
    Traceback (most recent call last):
      File "/Users/buildbot-sage/worker/sage_git/build/src/sage/doctest/forker.py", line 734, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/Users/buildbot-sage/worker/sage_git/build/src/sage/doctest/forker.py", line 1158, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.repl.ipython_kernel.install.SageKernelSpec.check[1]>", line 1, in <module>
        SageKernelSpec.check()  # random
        ^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/buildbot-sage/worker/sage_git/build/src/sage/repl/ipython_kernel/install.py", line 272, in check
        if Path(kernel_executable).resolve() != Path(sys.executable).resolve():
           ^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/buildbot-sage/worker/sage_git/build/local/var/lib/sage/venv-python3.12.5/lib/python3.12/pathlib.py", line 1162, in __init__
        super().__init__(*args)
      File "/Users/buildbot-sage/worker/sage_git/build/local/var/lib/sage/venv-python3.12.5/lib/python3.12/pathlib.py", line 373, in __init__
        raise TypeError(
    TypeError: argument should be a str or an os.PathLike object where __fspath__ returns a str, not 'NoneType'
**********************************************************************
1 item had failures:
   1 of   3 in sage.repl.ipython_kernel.install.SageKernelSpec.check
    [35 tests, 1 failure, 0.17s wall]
**********************************************************************

[kwankyu]

Added "return" after "warning".