chore(deps): update actions/checkout action to v7 #3366

Job	Run time
Integration Tests (pdm.minimal.lock)	34s
test_min_deps (macos-latest)	26s
Integration Tests (pdm.lock)	24s
test (3.12, macos-latest)	35s
test (3.13, macos-latest)	44s
test (3.11, windows-latest)	1m 15s
test (3.14, windows-latest)	1m 48s
test (3.12, windows-latest)	1m 15s
test (3.12, ubuntu-latest)	49s
test (3.14, macos-latest)	33s
test (3.11, ubuntu-latest)	53s
test (3.14, ubuntu-latest)	55s
test (3.13, windows-latest)	1m 50s
test_min_deps (ubuntu-latest)	31s
test_min_deps (windows-latest)	1m 8s
test (3.11, macos-latest)	32s
test (3.13, ubuntu-latest)	1m 5s
Combine & check coverage	10s
	15m 27s

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