Speed up test setup (#118) #483

Job	Run time
ctest (Release)	10m 15s
build-plugins (shrapnel, Release)	8m 4s
ctest (Debug)	8m 40s
build-plugins (shrapnel, Debug)	6m 44s
build-firmware	4m 50s
ctest-sanitize (Release)	17m 38s
flutter-analyze	2m 18s
ctest-sanitize (Debug)	10m 55s
flutter-format	1m 28s
flutter-test	2m 10s
license-headers	43s
coveralls-finish	4s
	1h 13m 49s

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