Fix compatibility with pytest-run-parallel and add free-threaded CI jobs #343

Job	Run time
tests / Load tox environments	10s
tests / py39-test-pytest62 (windows-latest)	1m 30s
tests / py312-test-pytest74 (windows-latest)	1m 19s
tests / py311-test-pytest73 (macos-latest)	37s
tests / py310-test-pytest62 (ubuntu-latest)	37s
tests / py313-test-pytest90 (ubuntu-latest)	37s
tests / codestyle (ubuntu-latest)	12s
tests / py310-test-pytest70 (macos-latest)	40s
tests / py310-test-pytest71 (windows-latest)	1m 26s
tests / py313-test-pytest83 (ubuntu-latest)	43s
tests / py311-test-pytest72 (ubuntu-latest)	38s
tests / py313-test-parallel (ubuntu-latest)	39s
tests / py314t-test-parallel (ubuntu-latest)	2m 14s
tests / py314t-test (ubuntu-latest)	2m 18s
tests / py313-test-devdeps (ubuntu-latest)	1m 11s
publish / Build source and wheel distribution	1m 18s
tests / report overall test coverage	0s
	16m 9s

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