ci: bump actions/checkout from 4.1.5 to 4.1.6 #529

Job	Run time
Build documentation	15s
Build and check benchmarks	1m 9s
Linux/ARM - Release tests (i686-unknown-linux-gnu)	1m 54s
Linux/ARM - Release tests (armv7-unknown-linux-gnueabihf)	2m 28s
no_std build (stable)	1m 6s
Linux/ARM - Release tests (powerpc64-unknown-linux-gnu)	2m 8s
Tests w. sanitizers	1m 23s
no_std build (nightly)	1m 19s
test (stable, ubuntu-latest)	4m 7s
test (stable, macos-latest)	3m 19s
WebAssembly - Release build (wasm32-unknown-unknown)	11s
test (stable, windows-latest)	7m 54s
test (beta, ubuntu-latest)	4m 8s
test (beta, macos-latest)	3m 20s
test (beta, windows-latest)	7m 23s
test (nightly, ubuntu-latest)	3m 57s
test (nightly, macos-latest)	3m 47s
test (nightly, windows-latest)	7m 33s
test (1.74.0, ubuntu-latest)	4m 21s
test (1.74.0, macos-latest)	10m 22s
test (1.74.0, windows-latest)	7m 25s
	1h 19m 29s

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