ci: extract messages periodically

Switch the updates of the translation catalog from after every push to
every 2 days at 6am UTC.

Considering that the update-translation-pot will commit the catalog only
if changed, and that there are usually not that many changes upstream,
it is simpler to update the translation catalog only every couple of
days.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Pino Toscano <ptoscano@redhat.com>

.github/workflows/ci.yml

@@ -1,8 +1,9 @@
 name: CI
 
 on:
-  push:
-    branches: [master]
+  schedule:
+    # every two days at 6:00 UTC
+    - cron: '0 6 */2 * *'
 
 jobs: