[gtk] (5 commits) Non-fast-forward update to branch matthiasc/for-master

[Matthias Clasen <matthiasc src gnome org>]

The branch 'matthiasc/for-master' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  fd63193... transition demo: Make buttons symbolic

Commits added to the branch:

  0e5dac8... meson: Change introspection option to yielding feature (*)
  5b89253... Use correct child widget when measuring (*)
  5a3aed8... Merge branch 'introspection' into 'master' (*)
  9c3c06d... transition demo: Make buttons symbolic
  740b34c... ci: Really enable werror

(*) This commit already existed in another branch; no separate mail sent