build

Fix clippy `unexpected_cfgs` warning with recent nightly #273

Job	Run time
clippy	42s
codecov	2m 47s
fmt	29s
build (stable, --features "")	42s
build (stable, --all-features)	1m 41s
build (stable, --no-default-features)	41s
semver	1m 29s
minimal-versions	51s
test	1m 40s
build (1.75, --features "")	39s
build (1.75, --all-features)	1m 41s
build (1.75, --no-default-features)	49s
build (beta, --features "")	44s
build (beta, --all-features)	1m 44s
build (beta, --no-default-features)	1m 7s
build (nightly, --features "")	1m 5s
build (nightly, --all-features)	1m 39s
build (nightly, --no-default-features)	38s
	21m 8s

Provide feedback