Use Python 3.12 in dev (#1198) #692

Job	Run time
Build docs & run doctests	32s
Tests & Mypy on 3.7	39s
Verify dev env (ubuntu-latest)	24s
Tests & Mypy on 3.8	1m 23s
Check types using pyright	40s
Verify dev env (windows-latest)	53s
Tests & Mypy on 3.9	1m 37s
Tests & Mypy on 3.10	1m 26s
Tests & Mypy on 3.11	1m 52s
Tests & Mypy on 3.12	1m 54s
Tests & Mypy on pypy-3.8	1m 7s
Tests & Mypy on pypy-3.9	1m 2s
Tests & Mypy on pypy-3.10	58s
Combine & check coverage.	12s
required-checks-pass	2s
	14m 41s

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