Test

Use ubuntu20-cache, --build-cache=on #204

Job	Run time
multiple-arch-armv7	12m 41s
cygwin64-cache	4m 32s
multiple-arch-aarch64	12m 3s
utest-regression-blackbox-test	1m 28s
fast	1s
cygwin64	8m 25s
build-centos7	1m 18s
build-cross-aarch64	3m 35s
build-cross-arm	2m 25s
build-ubuntu18	1m 32s
build-ubuntu16	1m 14s
build-ubuntu20	1m 8s
coverage	1m 56s
multiple-arch-amd64	1m 13s
test-done	0s
	53m 31s

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