fix: Fix VP9 codec checks on Mac Firefox (#4391)
fix: Fix VP9 codec checks on Mac Firefox (#4391)

Tests for VP9 codec checks were failing on Firefox on our M1 Mac.  This
addresses the issue by changing some default values that get used in a testing
environment, and another default value that is used in production.
shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player