gh-144981: Make PyUnstable_Code_SetExtra/GetExtra thread-safe (#144980) #2256

Job	Run time
x86_64-apple-darwin/clang	16m 43s
x86_64-pc-windows-msvc/msvc-free-threading	4m 27s
x86_64-unknown-linux-gnu/gcc-free-threading	8m 2s
x86_64-pc-windows-msvc/msvc	10m 9s
aarch64-apple-darwin/clang	9m 54s
aarch64-unknown-linux-gnu/gcc	7m 8s
x86_64-unknown-linux-gnu/gcc	9m 35s
	1h 5m 58s

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