chore(python): Update PyO3 to 0.21.0 #1099

Job	Run time
Verify commit messages	39s
Build on wasm32-unknown-unknown	1m 13s
Clippy	1m 17s
Run test coverage	1m 14s
Check features	56s
Rustfmt	12s
Generic pre-commit checks	24s
Python 3.7 on ubuntu-22.04	2m 18s
Python 3.8 on ubuntu-22.04	1m 58s
Test draft201909 (stable) on ubuntu-22.04	54s
Python 3.9 on ubuntu-22.04	1m 54s
Test draft202012 (stable) on ubuntu-22.04	1m 1s
Python 3.10 on ubuntu-22.04	1m 57s
Test draft201909 (stable) on macos-12	2m 35s
Python 3.11 on ubuntu-22.04	1m 56s
Test draft202012 (stable) on macos-12	2m 26s
Python 3.12 on ubuntu-22.04	2m 22s
Test draft201909 (stable) on windows-2022	5m 13s
Python 3.7 on macos-12	5m 53s
Test draft202012 (stable) on windows-2022	3m 32s
Python 3.8 on macos-12	4m 38s
Python 3.9 on macos-12	2m 40s
Python 3.10 on macos-12	5m 12s
Python 3.11 on macos-12	5m 4s
Python 3.12 on macos-12	5m 20s
Python 3.7 on windows-2022	5m 8s
Python 3.8 on windows-2022	5m 52s
Python 3.9 on windows-2022	5m 1s
Python 3.10 on windows-2022	4m 51s
Python 3.11 on windows-2022	5m 5s
Python 3.12 on windows-2022	4m 53s
	1h 33m 38s

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