Add depot caching to CI. Use scratchspace for test videos. Disable br… #262

Job	Run time
test (ubuntu-latest, x64, 1.6)	4m 4s
test (ubuntu-latest, x64, 1)	4m 3s
test (ubuntu-latest, x64, 1.10-nightly)	3m 53s
test (ubuntu-latest, x64, nightly)	2m 48s
test (ubuntu-latest, x86, 1.6)	4m 5s
test (ubuntu-latest, x86, 1)	3m 51s
test (ubuntu-latest, x86, 1.10-nightly)	4m 0s
test (ubuntu-latest, x86, nightly)	2m 53s
test (windows-latest, x64, 1.6)	11m 19s
test (windows-latest, x64, 1)	5m 44s
test (windows-latest, x64, 1.10-nightly)	5m 29s
test (windows-latest, x64, nightly)	4m 27s
test (windows-latest, x86, 1.6)	10m 42s
test (windows-latest, x86, 1)	6m 9s
test (windows-latest, x86, 1.10-nightly)	5m 12s
test (windows-latest, x86, nightly)	4m 5s
test (macOS-latest, x64, 1.6)	9m 9s
test (macOS-latest, x64, 1)	3m 57s
test (macOS-latest, x64, 1.10-nightly)	4m 26s
test (macOS-latest, x64, nightly)	4m 8s
	1h 44m 24s

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