Make run_tests.py suppressions flag fail with a clear error on unsupported platforms (#28235)
Make run_tests.py suppressions flag fail with a clear error on unsupported platforms (#28235)


jason-simmons/flutter_engine,devoncarew/engine,rmacnak-google/engine,jason-simmons/flutter_engine,rmacnak-google/engine,Hixie/sky_engine,flutter/engine,Hixie/sky_engine,flutter/engine,rmacnak-google/engine,flutter/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,devoncarew/engine,chinmaygarde/flutter_engine,rmacnak-google/engine,devoncarew/engine,aam/engine,rmacnak-google/engine,aam/engine,aam/engine,aam/engine,jason-simmons/flutter_engine,flutter/engine,jason-simmons/flutter_engine,Hixie/sky_engine,aam/engine,devoncarew/engine,devoncarew/engine,chinmaygarde/flutter_engine,Hixie/sky_engine,Hixie/sky_engine,chinmaygarde/flutter_engine,aam/engine,devoncarew/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,aam/engine,aam/engine,devoncarew/engine,flutter/engine,jason-simmons/flutter_engine,flutter/engine,rmacnak-google/engine,Hixie/sky_engine,Hixie/sky_engine,chinmaygarde/flutter_engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,flutter/engine,rmacnak-google/engine,Hixie/sky_engine,flutter/engine