gh-88118: Fix some test_multiprocessing flakiness. #105238

Job	Run time
Check for source changes	9s
Check if generated files are up to date	5m 12s
Docs	0s
Address sanitizer	7m 48s
Ubuntu SSL tests with OpenSSL (1.1.1w)	2m 1s
Hypothesis tests on Ubuntu	4m 58s
Ubuntu SSL tests with OpenSSL (3.0.13)	1m 54s
Ubuntu SSL tests with OpenSSL (3.1.5)	2m 3s
Ubuntu SSL tests with OpenSSL (3.2.1)	2m 4s
CIFuzz	0s
Windows / build and test (x64)	13m 40s
Windows / build (arm64)	2m 42s
Windows / build and test (x86)	14m 11s
Windows (free-threading) / build and test (x64)	28m 36s
Windows (free-threading) / build (arm64)	3m 20s
Windows (free-threading) / build and test (x86)	25m 54s
macOS / build and test (macos-14)	7m 40s
macOS (free-threading) / build and test (macos-14)	10m 20s
macOS (free-threading) / build and test (macos-13)	14m 50s
Ubuntu / build and test	6m 40s
macOS / build and test (macos-13)	11m 12s
Ubuntu (free-threading) / build and test	7m 50s
All required checks pass	2s
	2h 53m 6s

Provide feedback