matrix: use C locale for the synapse database

Synapse needs the database to be in C locale. Since v1.56.0, it refuses to start when this is not the case, see upgrade.md.

roles/matrix/tasks/main.yml

@@ -173,6 +173,9 @@
 
 - name: add synapse postgres db
   postgresql_db: db=synapse
+  lc_collate: C
+  lc_ctype: C
+  template: template0
   become: true
   become_user: postgres
   become_method: su