GH-65238: Add test cases for trailing slash handling in pathlib #96929

Job	Run time
Check for source changes	11s
Check if generated files are up to date	4m 23s
Docs	0s
Address sanitizer	6m 45s
Ubuntu SSL tests with OpenSSL (1.1.1w)	2m 10s
Hypothesis tests on Ubuntu	4m 18s
CIFuzz	0s
Ubuntu SSL tests with OpenSSL (3.0.11)	2m 26s
Ubuntu SSL tests with OpenSSL (3.1.3)	2m 8s
Windows / build and test (x64)	14m 2s
Windows / build and test (x86)	13m 19s
Windows / build (arm64)	3m 15s
Windows (free-threaded) / build and test (x64)	17m 19s
Windows (free-threaded) / build and test (x86)	16m 7s
Windows (free-threaded) / build (arm64)	3m 11s
macOS / build and test	19m 17s
macOS (free-threaded) / build and test	22m 10s
Ubuntu / build and test	6m 45s
Ubuntu (free-threaded) / build and test	7m 32s
All required checks pass	2s
	2h 25m 20s

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