Test

Use ubuntu20-cache, --build-cache=on, --ffmpeg-opus=off #209

Job	Run time
utest-regression-blackbox-test	5m 10s
multiple-arch-aarch64	9m 27s
cygwin64-cache	2m 46s
multiple-arch-armv7	8m 23s
fast	1s
cygwin64	8m 9s
build-ubuntu18	2m 45s
build-ubuntu20	3m 2s
build-centos7	2m 8s
build-cross-arm	3m 35s
build-cross-aarch64	2m 17s
build-ubuntu16	1m 40s
coverage	2m 23s
multiple-arch-amd64	1m 22s
test-done	1s
	53m 9s

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