[dependencies] Update actions/checkout digest to b4ffde6 #2211

Job	Run time
Debug build (Go 1.20)	25s
Debug build (Go 1.18)	39s
Debug build	26s
cross (windows-amd64, windows, amd64, v1)	37s
cross (windows-amd64-v3, windows, amd64, v3)	47s
cross (windows-386, windows, 386)	37s
cross (windows-arm64, windows, arm64)	42s
cross (windows-arm32v7, windows, arm, 7)	1m 10s
cross (linux-amd64, linux, amd64, v1)	1m 11s
cross (linux-amd64-v3, linux, amd64, v3)	1m 16s
cross (linux-386, linux, 386)	36s
cross (linux-arm64, linux, arm64)	1m 8s
cross (linux-armv5, linux, arm, 5)	58s
cross (linux-armv6, linux, arm, 6)	1m 8s
cross (linux-armv7, linux, arm, 7)	43s
cross (linux-mips-softfloat, linux, mips, softfloat)	43s
cross (linux-mips-hardfloat, linux, mips, hardfloat)	43s
cross (linux-mipsel-softfloat, linux, mipsle, softfloat)	44s
cross (linux-mipsel-hardfloat, linux, mipsle, hardfloat)	1m 8s
cross (linux-mips64, linux, mips64)	1m 16s
cross (linux-mips64el, linux, mips64le)	1m 9s
cross (linux-s390x, linux, s390x)	1m 9s
cross (darwin-amd64, darwin, amd64, v1)	45s
cross (darwin-amd64-v3, darwin, amd64, v3)	57s
cross (darwin-arm64, darwin, arm64)	1m 17s
cross (freebsd-amd64, freebsd, amd64, v1)	37s
cross (freebsd-amd64-v3, freebsd, amd64, v3)	1m 27s
cross (freebsd-386, freebsd, 386)	41s
cross (freebsd-arm64, freebsd, arm64)	1m 10s
	26m 9s

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