[ci] Only run with min and max supported Flutter SDK version #159

Job	Run time
Build iOS (2.10.5)	3m 48s
Build Android on Ubuntu (2.10.5)	2m 28s
Build macOS (2.10.5)	4m 31s
Build Android on Windows (2.10.5)	4m 26s
Build iOS (3.x)	4m 36s
Build macOS (3.x)	4m 53s
Build Android on Ubuntu (3.x)	2m 10s
Build Android on Windows (3.x)	4m 22s
Build Web on Ubuntu (2.10.5)	1m 56s
pub.dev scores check	1m 45s
Flutter code style check	52s
Build Web on Ubuntu (3.x)	1m 37s
Build Windows (2.10.5)	5m 6s
Build Windows (3.x)	5m 34s
android integration test	11m 19s
ios integration test	7m 26s
ios integration test with use_frameworks	7m 55s
macos integration test	3m 2s
windows integration test	4m 31s
pub publish check	1m 7s
Run flutter unit test (2.10.5)	1m 36s
Run flutter unit test (3.x)	1m 19s
Run flutter unit test web (2.10.5)	1m 33s
Run flutter unit test web (3.x)	1m 17s
	1h 29m 9s

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