Fix missing kwargs in some methods (#236)

## Issue
There are some inconsistencies with shared files with mysql-router vm
(see [PR
143](canonical/mysql-router-operator#143)

## Solution
Fix inconsistencies

src/kubernetes_upgrade.py

@@ -241,7 +241,7 @@ def determine_partition() -> int:
     def authorized(self) -> bool:
         raise Exception("Not supported on Kubernetes")
 
-    def upgrade_unit(self, *, workload_: workload.Workload, tls: bool) -> None:
+    def upgrade_unit(self, *, event, workload_: workload.Workload, tls: bool) -> None:
         raise Exception("Not supported on Kubernetes")
 
 

src/upgrade.py

@@ -223,7 +223,7 @@ def authorized(self) -> bool:
         """
 
     @abc.abstractmethod
-    def upgrade_unit(self, *, workload_: workload.Workload, tls: bool) -> None:
+    def upgrade_unit(self, *, event, workload_: workload.Workload, tls: bool) -> None:
         """Upgrade this unit.
 
         Only applies to machine charm

src/workload.py

@@ -430,7 +430,7 @@ def upgrade(
         if enabled:
             logger.debug("Disabling MySQL Router service before upgrade")
             self._disable_router()
-        super().upgrade(unit=unit, tls=tls, exporter_config=exporter_config)
+        super().upgrade(event=event, unit=unit, tls=tls, exporter_config=exporter_config)
         if enabled:
             logger.debug("Re-enabling MySQL Router service after upgrade")
             self._enable_router(event=event, tls=tls, unit_name=unit.name)