Speed up test setup #481

Job	Run time
build-firmware	4m 53s
build-plugins (shrapnel, Release)	8m 2s
ctest-sanitize (Release)	18m 28s
ctest (Release)	10m 9s
build-plugins (shrapnel, Debug)	6m 52s
ctest-sanitize (Debug)	10m 46s
ctest (Debug)	8m 46s
flutter-analyze	2m 4s
flutter-format	1m 48s
flutter-test	2m 17s
license-headers	46s
coveralls-finish	2s
	1h 14m 53s

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