Enable testing merge queues @ GitHub Actions CI/CD (#1195) #687

Job	Run time
Build docs & run doctests	44s
Check types using pyright	35s
Verify dev env (ubuntu-latest)	19s
Tests & Mypy on 3.7	1m 3s
Verify dev env (windows-latest)	53s
Tests & Mypy on 3.8	1m 26s
Tests & Mypy on 3.9	1m 16s
Tests & Mypy on 3.10	1m 51s
Tests & Mypy on 3.11	2m 18s
Tests & Mypy on 3.12	1m 30s
Tests & Mypy on pypy-3.8	1m 1s
Tests & Mypy on pypy-3.9	1m 2s
Tests & Mypy on pypy-3.10	1m 13s
Combine & check coverage.	18s
required-checks-pass	2s
	15m 31s

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