Allow new warning on recent nightly versions #644

Job	Run time
Check doc	1m 5s
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	2m 8s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	55s
test-ios	35s
test-miri	2m 49s
test-no-std	13s
test (macos-latest, x86_64-apple-darwin, stable)	1m 40s
test (windows-latest, x86_64-pc-windows-gnu, stable)	3m 13s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 42s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	3m 38s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	1m 58s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	1m 26s
	21m 22s

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