file-monitor: Explicitly cancel GFileMonitor before unreffing it
file-monitor: Explicitly cancel GFileMonitor before unreffing it

We need to explicitly cancel our file monitors currently before
decreasing their reference count, because otherwise the next create file
monitor may deadlock due to the GLib-internal worker thread also holding
a strong reference to the monitor.

See this GLib issue for more details:
https://gitlab.gnome.org/GNOME/glib/-/issues/1941

ximion/appstream,ximion/appstream,ximion/appstream,ximion/appstream