Fix nonblocking setting in `parallel::job_token` #1070

Job	Run time
Test aarch64-apple-tvos	1m 50s
MSRV (ubuntu-latest)	22s
Test CUDA support	1m 3s
MSRV (windows-latest)	37s
Clippy	18s
Rustfmt	7s
Test (stable)	40s
Test (beta)	32s
Test (nightly)	30s
Test (linux32)	40s
Test (macos)	41s
Test (aarch64-ios)	47s
Test (win32)	35s
Test (win64)	37s
Test (mingw32)	36s
Test (mingw64)	36s
Test (windows-2019)	36s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	34s
	11m 41s

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