Only accept GDrive notifications if the content was updated

Signed-off-by: Emmy D'Anello <emmy.danello@animath.fr>

participation/views.py

@@ -1893,6 +1893,10 @@ class GSheetNotificationsView(View):
         if request.headers['X-Goog-Channel-ID'] != expected_channel_id:
             raise ValueError(f"Invalid channel ID: {request.headers['X-Goog-Channel-ID']}")
 
+        if request.headers['X-Goog-Resource-State'] != 'update' \
+                or 'content' not in request.headers['X-Goog-Changed'].split(','):
+            return HttpResponse(status=204)
+
         # Run the parsing in dedicated executors since it takes time
         executor = ThreadPoolExecutor()
         async for pool in tournament.pools.prefetch_related('participations', 'passages__notes', 'juries').all():