ci: Check that retro-gtk.h contains public headers

This will check we don't accidentally forget to add public headers to
public retro-gtk.h.
5 jobs for prepare-0-18-1 in 4 minutes and 7 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Lint
passed #559793
api-visibility

00:00:18

 
  Build
passed #559794
flatpak:demo

00:01:40

 
  Test
passed #559795
flatpak:tests

00:01:45

 
  Review
passed #559796
review

00:00:23

manual #559797
allowed to fail manual
stop_review