[test] Fixes testing/run_tests.py py3 support. (#29611)
[test] Fixes testing/run_tests.py py3 support. (#29611)


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