Cache compiler versions detected #910

Job	Run time
Test CUDA support	24s
MSRV (ubuntu-latest)	32s
MSRV (windows-latest)	45s
Test aarch64-apple-tvos	3m 23s
Rustfmt	13s
Test (stable)	27s
Test (beta)	26s
Test (nightly)	26s
Test (linux32)	1m 5s
Test (macos)	47s
Test (aarch64-ios)	42s
Test (win32)	1m 9s
Test (win64)	1m 0s
Test (mingw32)	1m 25s
Test (mingw64)	1m 32s
Test (windows-2019)	1m 23s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	1m 46s
	17m 25s

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