cogl/tests: Use less verbose run-tests.sh on single tests run by meson

Use less verbose output when run-tests.sh is running only a test and we're
requested for less verbose output.

GNOME/mutter!442
Status Job ID Name Coverage
  Build
passed #263830
build-mutter

00:01:22

 
  Test
passed #263831
test-mutter

00:03:38