Fix bug with RainMachine update entity (#78411)

* Fix bug with RainMachine update entity

* Comment

homeassistant/components/rainmachine/update.py

@@ -99,4 +99,11 @@ class RainMachineUpdateEntity(RainMachineEntity, UpdateEntity):
             UpdateStates.UPGRADING,
             UpdateStates.REBOOT,
         )
-        self._attr_latest_version = data["packageDetails"]["newVersion"]
+
+        # The RainMachine API docs say that multiple "packages" can be updated, but
+        # don't give details on what types exist (which makes it impossible to have
+        # update entities per update type); so, we use the first one (with the idea that
+        # after it succeeds, the entity will show the next update):
+        package_details = data["packageDetails"][0]
+        self._attr_latest_version = package_details["newVersion"]
+        self._attr_title = package_details["packageName"]