docs: fix simple typo, unncessary -> unnecessary

There is a small typo in Orange/widgets/visualize/utils/scene.py.

Should read `unnecessary` rather than `unncessary`.

Author: timgates42

Orange/widgets/visualize/utils/scene.py

@@ -10,7 +10,7 @@ class UpdateItemsOnSelectGraphicsScene(QGraphicsScene):
 
     Notes
     -----
-    .. note:: I suspect this is completely unncessary, but have not been able
+    .. note:: I suspect this is completely unnecessary, but have not been able
         to find a reasonable way to keep the selection logic inside the actual
         `QGraphicsItem` objects