Bump actions/checkout from 6 to 7 in the dependencies group #2608

Job	Run time
linux (swiftlang/swift:nightly-6.4.x-noble)	6m 44s
linux (swift:6.2)	4m 52s
linux (swift:6.1)	4m 46s
linux (swift:6.3)	5m 9s
macOS	2m 23s
	23m 54s

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