GH-89727: Fix FD leak on `os.fwalk()` generator finalization. #114308

Job	Run time
Check for source changes	14s
Check if generated files are up to date	5m 55s
Docs	0s
Address sanitizer	8m 12s
Ubuntu SSL tests with OpenSSL (1.1.1w)	1m 52s
Hypothesis tests on Ubuntu	5m 22s
Ubuntu SSL tests with OpenSSL (3.0.13)	1m 57s
CIFuzz	0s
Ubuntu SSL tests with OpenSSL (3.1.5)	2m 7s
Ubuntu SSL tests with OpenSSL (3.2.1)	1m 55s
Windows / build and test (x64)	16m 41s
Windows / build and test (x86)	17m 47s
Windows / build (arm64)	3m 48s
macOS (free-threading) / build and test (macos-14)	7m 24s
macOS / build and test (macos-14)	9m 0s
macOS / build and test (macos-13)	14m 43s
Thread sanitizer / Thread sanitizer	3m 28s
Thread sanitizer (free-threading) / Thread sanitizer	7m 6s
Windows (free-threading) / build and test (x64)	19m 51s
Windows (free-threading) / build (arm64)	4m 10s
Windows (free-threading) / build and test (x86)	24m 10s
Ubuntu / build and test	6m 48s
Ubuntu (free-threading) / build and test	10m 26s
WASI / build and test	10m 46s
All required checks pass	3s
	3h 3m 45s

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