[bubbles] issue when using duplicated metrics (#7087)

superset/viz.py

@@ -954,11 +954,11 @@ class BubbleViz(NVD3Viz):
         self.series = form_data.get('series') or self.entity
         d['row_limit'] = form_data.get('limit')
 
-        d['metrics'] = [
+        d['metrics'] = list(set([
             self.z_metric,
             self.x_metric,
             self.y_metric,
-        ]
+        ]))
         if not all(d['metrics'] + [self.entity]):
             raise Exception(_('Pick a metric for x, y and size'))
         return d