chore: remove f-string in logging call (#1234)

Use lazy interpolation in `logging.*` calls.

Missed in #1227, because I didn't think to enable multi-line searching,
and this logging call wraps the f-string on to the next line.

ops/framework.py

@@ -951,9 +951,9 @@ def _reemit(self, single_event_path: Optional[str] = None):
 
             else:
                 logger.warning(
-                    f'Reference to ops.Object at path {observer_path} has been garbage collected '
+                    'Reference to ops.Object at path %s has been garbage collected '
                     'between when the charm was initialised and when the event was emitted. '
-                    'Make sure sure you store a reference to the observer.'
+                    'Make sure sure you store a reference to the observer.', observer_path
                 )
 
             if event.deferred: