Fix compatibility with pytest-run-parallel and add free-threaded CI jobs #338

Job	Run time
tests / Load tox environments	9s
tests / py39-test-pytestoldest (windows-latest)	1m 29s
tests / py312-test-pytest74 (windows-latest)	1m 22s
tests / py313-test-parallel (ubuntu-latest)	48s
tests / py310-test-pytest62 (ubuntu-latest)	52s
tests / py310-test-pytest70 (macos-latest)	48s
tests / py39-test-pytest61 (windows-latest)	1m 19s
tests / codestyle (ubuntu-latest)	17s
tests / py313t-test (ubuntu-latest)	2m 22s
tests / py39-test-pytest60 (macos-latest)	50s
tests / py39-test-pytest53 (ubuntu-latest)	43s
tests / py313-test-pytest83 (ubuntu-latest)	43s
tests / py313-test-pytest90 (ubuntu-latest)	43s
tests / py313t-test-parallel (ubuntu-latest)	2m 41s
tests / py313-test-devdeps (ubuntu-latest)	58s
tests / py311-test-pytest73 (macos-latest)	34s
tests / py311-test-pytest72 (ubuntu-latest)	37s
tests / py310-test-pytest71 (windows-latest)	2m 6s
publish / Build source and wheel distribution	1m 15s
tests / report overall test coverage	0s
	20m 36s

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