[GTKUI] Support using the Ayatana fork of indicators.

As this fork is maintained in Debian, and as of Impish/21.10 is the supported
variant in Ubuntu as well.

Closes: deluge-torrent/deluge#317

deluge/ui/gtk3/systemtray.py

@@ -30,6 +30,10 @@ from .common import build_menu_radio_list, get_logo
 from .dialogs import OtherDialog
 
 try:
+    try:
+        require_version('AyatanaAppIndicator3', '0.1')
+        from gi.repository import AyatanaAppIndicator3 as AppIndicator3
+    except (ValueError, ImportError):
         require_version('AppIndicator3', '0.1')
         from gi.repository import AppIndicator3
 except (ValueError, ImportError):