gst-inspect: Use only original 16 colors

Not only this will make colored output work on old terminals and console
as well, terminals can theme the actual colors this way to make it fit
with their different themes this way.
3 jobs for inspect-16-colors in 5 minutes and 49 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Preparation
passed manifest #50974

00:00:19

 
  Build
passed build fedora x86_64 #50975

00:03:14

 
  Full Builds
passed build android arm64 api28 #50976

00:02:15