FileChooser: Fix deprecation warnings

Fixes PyGIDeprecationWarning: GObject.GError is deprecated
and button initialization, see: https://wiki.gnome.org/action/show/Projects/PyGObject/
InitializerDeprecations?action=show&redirect=PyGObject%2FInitializerDeprecations
3 jobs for fix-filechooser-deprecation-warning in 3 minutes and 15 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #11560
run-appdata

00:00:08

passed #11559
run-tests

00:02:54

 
  Build
passed #11561
run-build

00:00:12