Destroying the source from an action callback will result in the
notification being destroyed twice:
- source.destroy() destroys all its notifications
- a notification destroys itself after an action
was activated
This results in unwanted log spam when attempting to dispose the
notification for a second time.
There is actually no good reason for destroying the source explicitly,
as sources already self-destruct with their last notification.
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/4457
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1908>
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