tests: examples: gl: gtk: Disabled on MacOS X

It fails to build on MacOS X. This example should be disabled
until fixed.

Issue: #518
6 jobs for fix-link-failure-on-macosx in 30 minutes and 45 seconds (queued for 32 seconds)
Status Job ID Name Coverage
  Preparation
passed #63107
gst indent

00:00:32

passed #63106
manifest

00:00:22

 
  Build
passed #63108
build fedora x86_64

00:04:34

 
  Test
passed #63109
check fedora

00:15:32

 
  Full Builds
passed #63110
build android arm64 api28

00:02:17

passed #63111
build cerbero fedora x86_64

00:09:45