Fix compatibility with pytest-run-parallel and add free-threaded CI jobs #341

Job	Run time
tests / Load tox environments	7s
tests / py311-test-pytest73 (macos-latest)	31s
tests / py39-test-pytest53 (ubuntu-latest)	38s
tests / py310-test-pytest71 (windows-latest)	1m 26s
tests / codestyle (ubuntu-latest)	12s
tests / py39-test-pytest60 (macos-latest)	42s
tests / py313t-test-parallel (ubuntu-latest)	2m 28s
tests / py313-test-parallel (ubuntu-latest)	40s
tests / py310-test-pytest70 (macos-latest)	39s
tests / py313-test-pytest83 (ubuntu-latest)	39s
tests / py311-test-pytest72 (ubuntu-latest)	44s
tests / py313t-test (ubuntu-latest)	2m 17s
tests / py39-test-pytest61 (windows-latest)	1m 14s
tests / py310-test-pytest62 (ubuntu-latest)	39s
tests / py313-test-devdeps (ubuntu-latest)	57s
tests / py39-test-pytestoldest (windows-latest)	1m 31s
tests / py313-test-pytest90 (ubuntu-latest)	43s
tests / py312-test-pytest74 (windows-latest)	1m 18s
tests / report overall test coverage	-1s
publish	0s
	17m 24s

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