fix(test): retrofit deprecations

pathlib support and sphinx.testing.path deprecation in Sphinx ver. 9  was
announced in Sphinx ver. 6 and enabled in Sphinx ver. 7, hence there are three
different environment states to support in regards to paths in Sphinx testing
environments.

tests/integration/byteb4rb1e/sphinxcontrib/testing/pytest/test_fixtures.py

@@ -1,3 +1,4 @@
+from pathlib import Path
 
 import pytest
 
@@ -26,6 +27,6 @@ def test_mock_sphinx_testapp(mock_sphinx_testapp, mock_sphinx_testsrc_dir):
     app = mock_sphinx_testapp(srcdir=srcdir)
 
     assert app.builder is not None
-    assert app.srcdir.samefile(srcdir) is False  # Should be copied to internal src
+    assert Path(app.srcdir).samefile(srcdir) is False  # Should be copied to internal src
 
     app.build(force_all=True)