ci: update `actions/checkout` to v4 #150

Job	Run time
Minimum supported rust version	1m 4s
Code quality	31s
Build for linux-gnu	59s
Build for win-gnu	3m 48s
Build for win-msvc	3m 45s
Build for win32-msvc	2m 41s
Build for macos	2m 51s
	15m 39s

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