[gtk] (8 commits) Non-fast-forward update to branch headless-seatless

[Matthias Clasen <matthiasc src gnome org>]

The branch 'headless-seatless' 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:

  6fa6443... gtk: Handle seatless displays
  a5def45... docs: Clarify gdk_display_get_default_seat() docs
  aa8c7ee... ci: Add weston and weston-libs to the fedora image
  4f55c01... ci: Fix a typo in the run-docker.sh script
  ed300d1... tests: Allow setting a subdir for output
  2b6735e... testsuite: Add test setups for backends
  cb6c7b3... ci: Run tests with different backends

Commits added to the branch:

  01acb9f... gtk: Handle seatless displays
  223eee1... docs: Clarify gdk_display_get_default_seat() docs
  e80fc7b... ci: Add weston and weston-libs to the fedora image
  074439c... ci: Fix a typo in the run-docker.sh script
  4fe6af3... tests: Allow setting a subdir for output
  ff592a7... testsuite: Add test setups for backends
  468c228... ci: Run tests with different backends
  c0027a7... tests: Centralize our test setup a bit