Bump actions/checkout from 3 to 4 #1491

Job	Run time
MSRV (ubuntu-latest)	23s
Test (stable)	34s
MSRV (windows-latest)	37s
Test (beta)	29s
Test (nightly)	1m 10s
Clippy	12s
Test (linux32)	1m 21s
Test build-std (aarch64-tvos)	1m 36s
Test CUDA support	31s
Test build-std (aarch64-tvos-sim)	1m 48s
Test (macos)	2m 32s
Rustfmt	12s
Test (aarch64-macos)	1m 10s
Test build-std (x86_64-tvos)	1m 59s
Test (aarch64-ios)	39s
Test (win32)	1m 29s
semver-checks	16s
Test (win64)	1m 27s
Test (mingw32)	1m 41s
Test (mingw64)	1m 39s
Test (windows-2019)	2m 1s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	2m 25s
Test (windows-clang, windows-2019, stable, x86_64-pc-windows-msvc, clang, clang++)	2m 58s
Test (windows-clang-cl, windows-2019, stable, x86_64-pc-windows-msvc, clang-cl, clang-cl)	2m 19s
	31m 28s

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