Fix upgrade on leader unit after resume-upgrade (#132)

If `resume-upgrade` ran and leader was 2nd highest unit, it would not
upgrade on the same event

Leftover from k8s where reconcile_partition triggers upgrade of unit
(and Juju event) automatically

Author: carlcsaposs-canonical

src/machine_charm.py

@@ -87,6 +87,11 @@ def _on_upgrade_charm(self, _) -> None:
             # Only call `reconcile` on leader unit to avoid race conditions with `upgrade_resumed`
             self.reconcile()
 
+    def _on_resume_upgrade_action(self, event: ops.ActionEvent) -> None:
+        super()._on_resume_upgrade_action(event)
+        # If next to upgrade, upgrade leader unit
+        self.reconcile()
+
     def _on_force_upgrade_action(self, event: ops.ActionEvent) -> None:
         if not self._upgrade or not self._upgrade.in_progress:
             message = "No upgrade in progress"