build: Revert PyO3 version back to `0.21` #12228

Job	Run time
check-wasm	6m 25s
check-features	9m 0s
integration-test (ubuntu-latest)	2m 4s
integration-test (windows-latest)	7m 10s
test (ubuntu-latest)	3m 56s
test (windows-latest)	10m 35s
	39m 10s

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