Test

Use ubuntu20, --build-cache=off #206

Job	Run time
multiple-arch-aarch64	11m 49s
multiple-arch-armv7	5m 42s
cygwin64-cache	3m 34s
utest-regression-blackbox-test	6m 19s
cygwin64	9m 29s
fast	1s
build-ubuntu18	1m 8s
build-centos7	59s
build-ubuntu20	1m 7s
build-cross-aarch64	3m 31s
build-cross-arm	4m 4s
build-ubuntu16	1m 29s
coverage	1m 58s
multiple-arch-amd64	1m 15s
test-done	0s
	52m 25s

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