chore(repo): excludes flutter/dart sdk beta testing on PRs #1187

Job	Run time
test / test-dart-vm (3.0.1)	2m 6s
test / test-dart-vm (stable)	2m 7s
ddc_test / test-dart-ddc (3.0.1, chrome)	2m 14s
native_test / test-dart-native (macos-latest)	2m 26s
ddc_test / test-dart-ddc (3.0.1, firefox)	2m 22s
native_test / test-dart-native (windows-latest)	2m 53s
ddc_test / test-dart-ddc (stable, chrome)	2m 13s
ddc_test / test-dart-ddc (stable, firefox)	2m 16s
dart2js_test / test-dart-2js (3.0.1, chrome)	3m 45s
dart2js_test / test-dart-2js (3.0.1, firefox)	3m 41s
dart2js_test / test-dart-2js (stable, chrome)	3m 47s
dart2js_test / test-dart-2js (stable, firefox)	4m 3s
	33m 53s

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