[pygobject] (8 commits) Non-fast-forward update to branch tree-model-sort-new-overrides

[Christoph Reiter <creiter src gnome org>]

The branch 'tree-model-sort-new-overrides' 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:

  cd71a5f... Gtk overrides: make sure TreeModelSort.new_with_model and T

Commits added to the branch:

  c10c985... pygobject-object: Avoid checking whether NULL is floating (*)
  28843cb... gtk overrides: Drop Menu, MenuItem for Gtk 4 (*)
  8045119... CI: install pycairo from pypi not git master (*)
  091b5eb... meson: track pycairo-1.18 branch in the pycairo subproject (*)
  4f4dab4... Doc: Remove reference to a fixed bug (*)
  ac3a69c... CI: update pip in the xenial job (*)
  e181d41... CI: use the "flatpak" tag for jobs using flatpak (*)
  0b1ff4d... Gtk overrides: make sure TreeModelSort.new_with_model and T

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