Fix nightly warning #21

Job	Run time
Test aarch64-apple-tvos	3m 22s
Test CUDA support	26s
MSRV (ubuntu-latest)	25s
Clippy	6s
MSRV (windows-latest)	45s
Test (stable)	19s
Rustfmt	5s
Test (beta)	26s
Test (nightly)	28s
Test (linux32)	44s
Test (macos)	37s
Test (aarch64-ios)	53s
Test (win32)	1m 36s
Test (win64)	2m 59s
Test (mingw32)	2m 6s
Test (mingw64)	1m 15s
Test (windows-2019)	2m 6s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	3m 33s
	22m 11s

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