Fix overwriting app config with model config

Author: johnsca

juju/model.py

@@ -1482,8 +1482,8 @@ async def deploy(
                     os.path.expanduser(entity_id))
                 series = series or get_charm_series(charm_dir)
                 if not series:
-                    config = await self.get_config()
-                    default_series = config.get("default-series")
+                    model_config = await self.get_config()
+                    default_series = model_config.get("default-series")
                     if default_series:
                         series = default_series.value
                 if not series: