PyGIWarning: Gst was imported without specifying a version first.

On launch when using macOS:

gajim/common/multimedia_helpers.py:19: PyGIWarning: Gst was imported without specifying a version first. Use gi.require_version('Gst', '1.0') before import to ensure that the right version gets loaded.

Possible fix (not sure if this should be here or in common/app.py, so I won't commit anything yet):

diff --git a/gajim/gtk/preferences.py b/gajim/gtk/preferences.py
index 897fef45e..83a0200cb 100644
--- a/gajim/gtk/preferences.py
+++ b/gajim/gtk/preferences.py
@@ -41,6 +41,8 @@ from gajim.gtk.proxies import ManageProxies
 from gajim.gtk.sounds import ManageSounds
 
 try:
+    import gi
+    gi.require_version('Gst', '1.0')
     from gajim.common.multimedia_helpers import AudioInputManager, AudioOutputManager
     from gajim.common.multimedia_helpers import VideoInputManager
     from gi.repository import Gst  # pylint: disable=ungrouped-imports