Fix CI by relaxing our MSRV constraint #2121

Job	Run time
aarch64_linux_native_builds (aarch64-unknown-linux-musl)	6h 0m 15s
x86_64_linux_native_builds (x86_64-unknown-linux-musl)	1m 40s
aarch64_linux_native_builds (aarch64-unknown-linux-gnu)	1m 22s
macos	1m 57s
x86_64_linux_native_builds (x86_64-unknown-linux-gnu)	1m 58s
tier3 (armv7-unknown-linux-uclibceabihf)	1m 10s
macos-aarch64	54s
rustfmt	7s
tier3 (x86_64-unknown-haiku)	1m 3s
solaris (x86_64-pc-solaris)	6m 23s
minver	17s
tier3 (x86_64-unknown-openbsd)	1m 4s
tier3 (x86_64-unknown-dragonfly)	1m 3s
cross	0s
msrv	0s
cross_compiling	0s
redox	0s
	6h 19m 13s

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