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
2 jobs for meson-test-suites in 5 minutes and 10 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #263835
build-mutter

00:01:41

 
  Test
passed #263836
test-mutter

00:03:29