fix: set tooltip on label as well (#711)

Author: tlambert03

src/magicgui/widgets/bases/_widget.py

@@ -328,7 +328,9 @@ def tooltip(self) -> str | None:
     @tooltip.setter
     def tooltip(self, value: str | None) -> None:
         """Set the tooltip for this widget."""
-        return self._widget._mgui_set_tooltip(value)
+        self._widget._mgui_set_tooltip(value)
+        if (lbl := self._labeled_widget()) is not None:
+            lbl._label_widget.tooltip = value
 
     def _labeled_widget(self) -> _LabeledWidget | None:
         """Return _LabeledWidget container, if applicable."""