python-Traits fails to build with Sphinx 7.2.6 on Fedora Rawhide (40+).

The issue detected:
```
ERROR: test_abbreviated_annotations (traits.util.tests.test_trait_documenter.TestTraitDocumenter.test_abbreviated_annotations)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/builddir/build/BUILD/traits-6.4.2/build/lib.linux-x86_64-cpython-312/traits/util/tests/test_trait_documenter.py", line 147, in test_abbreviated_annotations
    with self.create_directive() as directive:
  File "/usr/lib64/python3.12/contextlib.py", line 137, in __enter__
    return next(self.gen)
           ^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/traits-6.4.2/build/lib.linux-x86_64-cpython-312/traits/util/tests/test_trait_documenter.py", line 226, in create_directive
    app = SphinxTestApp(srcdir=path(tmpdir))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/sphinx/testing/util.py", line 105, in __init__
    outdir.mkdir(parents=True, exist_ok=True)
    ^^^^^^^^^^^^
AttributeError: 'path' object has no attribute 'mkdir'. Did you mean: 'isdir'?

======================================================================
ERROR: test_can_document_member (traits.util.tests.test_trait_documenter.TestTraitDocumenter.test_can_document_member)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/builddir/build/BUILD/traits-6.4.2/build/lib.linux-x86_64-cpython-312/traits/util/tests/test_trait_documenter.py", line 177, in test_can_document_member
    with self.create_directive() as directive:
  File "/usr/lib64/python3.12/contextlib.py", line 137, in __enter__
    return next(self.gen)
           ^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/traits-6.4.2/build/lib.linux-x86_64-cpython-312/traits/util/tests/test_trait_documenter.py", line 226, in create_directive
    app = SphinxTestApp(srcdir=path(tmpdir))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/sphinx/testing/util.py", line 105, in __init__
    outdir.mkdir(parents=True, exist_ok=True)
    ^^^^^^^^^^^^
AttributeError: 'path' object has no attribute 'mkdir'. Did you mean: 'isdir'?

----------------------------------------------------------------------
Ran 1648 tests in 38.014s

FAILED (errors=2, skipped=5)
```

From Sphinx' changelog: #11526: Deprecate sphinx.testing.path. Use os.path or pathlib instead.
https://www.sphinx-doc.org/en/master/changes.html

For the logs from testing build attempts, see:
https://copr.fedorainfracloud.org/coprs/ksurma/sphinx-7.2.6/package/python-Traits

You can test you package in mock running:

$ mock -r fedora-rawhide-x86_64 --addrepo=https://download.copr.fedorainfracloud.org/results/ksurma/sphinx-7.2.6/fedora-rawhide-x86_64/ --no-clean your.src.rpm
$ mock -r fedora-rawhide-x86_64 --addrepo=https://download.copr.fedorainfracloud.org/results/ksurma/sphinx-7.2.6/fedora-rawhide-x86_64/ shell

We'd like to include Sphinx 7.2.x in Fedora 40.

Let us know here if you have any questions. Thank You!