Opening the "Synchronization Services" window causes a traceback with AttributeError: 'Window' object has no attribute '_GTGCalendar__sigid'

[nekohayo]

Trying out #1191 which is only 2 commits atop of current git master, I accidentally clicked the "Synchronization Services" menu item in the main hamburger menu, and I got this empty window as a result:

… with this accompanying traceback:

Traceback (most recent call last):
  File "/app/lib/python3.12/site-packages/GTG/gtk/editor/calendar.py", line 157, in _esc_close
    self.close_calendar()
  File "/app/lib/python3.12/site-packages/GTG/gtk/editor/calendar.py", line 110, in close_calendar
    if self.__sigid is not None:
       ^^^^^^^^^^^^
  File "/app/lib/python3.12/site-packages/GTG/gtk/editor/calendar.py", line 151, in __getattr__
    return getattr(self.__window, attr)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Window' object has no attribute '_GTGCalendar__sigid'

I wonder if it's somehow related to @SqAtx's issue #1176, since both are about a "calendar" of some sort.

GTG: 0.7-dev-5bd604bb
Flatpak: 1.16.0
Snap: False
Display Name: wayland-0
Desktop: GNOME

lxml: True
caldav: True
Cheetah3: True
dbus-python: True
pdflatex: False
pypdftk: False

[nekohayo]

Otherwise I wonder if this is related to #784?