Enable testing merge queues @ GitHub Actions CI/CD #684

Job	Run time
Check types using pyright	41s
Build docs & run doctests	37s
Verify dev env (ubuntu-latest)	22s
Verify dev env (windows-latest)	1m 5s
Tests & Mypy on 3.7	55s
Tests & Mypy on 3.8	1m 33s
Tests & Mypy on 3.9	1m 40s
Tests & Mypy on 3.10	2m 3s
Tests & Mypy on 3.11	1m 36s
Tests & Mypy on 3.12	1m 18s
Tests & Mypy on pypy-3.8	1m 11s
Tests & Mypy on pypy-3.9	1m 21s
Tests & Mypy on pypy-3.10	1m 23s
Combine & check coverage.	0s
required-checks-pass	3s
	15m 48s

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