Pin to 3.12.4 (#635) #1214

Job	Run time
build-lint-test (3.8, ubuntu-latest)	14m 6s
build-lint-test (3.8, ubuntu-arm)	13m 38s
build-lint-test (3.8, macos-intel)	33m 49s
build-lint-test (3.8, windows-latest)	14m 57s
build-lint-test (3.12, ubuntu-latest)	14m 12s
build-lint-test (3.12, ubuntu-arm)	12m 52s
build-lint-test (3.12, macos-intel)	13m 42s
build-lint-test (3.12, macos-arm)	7m 9s
build-lint-test (3.12, windows-latest)	16m 51s
features-tests / test	6m 0s
	2h 27m 16s

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