DPE-7726: Fix topology obsert Primarly status removal

On topology observer event, the primary unit used to loose Primarly label.

Author: taurus-forever

src/charm.py

@@ -1332,7 +1332,7 @@ def _on_cluster_topology_change(self, _):
         logger.info("Cluster topology changed")
         if self.primary_endpoint:
             self._update_relation_endpoints()
-            self.set_unit_status(ActiveStatus())
+            self._set_primary_status_message()
 
     def _on_install(self, event: InstallEvent) -> None:
         """Install prerequisites for the application."""