Revert "Update pyo3 requirement from 0.21.1 to 0.22.0" #546

Job	Run time
Check	14s
Lints	23s
Test Suite (ubuntu-latest, MSRV)	2m 52s
Test Suite (ubuntu-latest, stable)	2m 39s
Test Suite (macos-latest, MSRV)	1m 48s
no-std build (aarch64-unknown-none)	23s
Test Suite (macos-latest, stable)	1m 47s
no-std build (thumbv6m-none-eabi)	23s
Test Suite (windows-latest, MSRV)	8m 42s
Test Suite (windows-latest, stable)	9m 27s
Coverage	40s
Release	0s
	29m 18s

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