Bump actions/checkout from 5 to 6 in the actions group #271

Job	Run time
test / Load tox environments	8s
test / py311-test-mpl38 (macos-latest)	1m 43s
test / py313-test-mpl310 (ubuntu-latest)	3m 21s
test / py311-test-mpl38 (windows-latest)	3m 11s
test / py311-test-mpl38 (ubuntu-latest)	2m 59s
test / py311-test-mpl39 (ubuntu-latest)	2m 47s
test / py312-test-mpl39 (ubuntu-latest)	3m 18s
test / py313-test-mpl310 (macos-latest)	2m 35s
test / py313-test-mpl310 (windows-latest)	3m 52s
test / py39-test-mpl35 (macos-latest)	3m 30s
test / py313-test-mpldev-pytestdev (ubuntu-latest)	3m 34s
test / py39-test-mpl33-pytest62 (ubuntu-latest)	3m 9s
test / py312-test-mpl310 (ubuntu-latest)	3m 18s
test / py311-test-mpl37-pytest74 (ubuntu-latest)	2m 52s
test / py39-test-mpl33 (ubuntu-latest)	2m 54s
test / py311-test-mpl310 (ubuntu-latest)	3m 1s
test / py39-test-mpl33 (windows-latest)	3m 45s
publish	0s
	49m 57s

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