More pythonic patch

Trying to please pydantic/validators.py from Github CI

sashimi/gui/camera_gui.py

@@ -164,18 +164,13 @@ def __init__(self, state: State, timer: QTimer, style: str):
             self.reset_contrast
         )
 
-        self.add_scale_bar_units(" um")
-
-    def add_scale_bar_units(self, units: str) -> None:
+        self.viewer.camera.events.zoom.connect(self.add_scale_bar_units)
 
+    def add_scale_bar_units(self, event: Event) -> None:
+        """Patch to display physical units in scale bar. Overrides _on_zoom_change() method"""
         scale_bar = self.viewer.window.qt_viewer.scale_bar
-        old_on_zoom_change = scale_bar._on_zoom_change
-
-        def _on_zoom_change(event: Event):
-            old_on_zoom_change(event)
-            scale_bar.text_node.text += units
-
-        scale_bar._on_zoom_change = _on_zoom_change
+        scale_bar._on_zoom_change(event)
+        scale_bar.text_node.text += " um"
 
     def get_fullframe_size(self):
         """Maximum size of the image at current binning. As stated above, we assume square sensors."""