[libadwaita] Non-fast-forward update to branch wip/exalm/oapcity

[Alexander Mikhaylenko <alexm src gnome org>]

The branch 'wip/exalm/oapcity' 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:

  d3524a9... stylesheet: Use square opacity for flat buttons

Commits added to the branch:

  de3d8ec... stylesheet: Use smaller opacity for disabled flat buttons