[glib] (8 commits) ...Merge branch 'freeze-shenanigans' into 'main'

[Philip Withnall <pwithnall src gnome org>]

Summary of changes:

  fb380b9... Add a testcase for notify-in-instance-init (*)
  9444ace... Unconditionally mark objects as in-construction (*)
  58ab960... Handle a corner-case of notify avoidance (*)
  dccab10... Add another testcase (*)
  b92f1fc... Handle notify freezing with custom constructors (*)
  10a1c16... Avoid atomics during construction (*)
  af7ba68... gobject: ifdef out some inline functions if they’re not use (*)
  2e1218e... Merge branch 'freeze-shenanigans' into 'main'

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