glamor: Fix debugging callback setup on GLES

You will not find GL_ARB_* extensions in a GLES context by definition,
the droid you're looking for is named GL_KHR_debug.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
4 jobs for glamor-gles-debugging in 7 minutes and 56 seconds (queued for 7 minutes and 31 seconds)
Status Job ID Name Coverage
  Docker Image
passed #4150796
debian-testing

00:00:25

 
  Build And Test
passed #4150797
autotools

00:06:32

passed #4150798
meson

00:01:02

passed #4150799
meson-noglamor

00:00:58