fix metrics type error in pivot table viz (#5025)

transfer metrics dict label to list of string

superset/viz.py

@@ -691,7 +691,7 @@ class PivotTableViz(BaseViz):
         df = df.pivot_table(
             index=self.form_data.get('groupby'),
             columns=self.form_data.get('columns'),
-            values=self.form_data.get('metrics'),
+            values=[self.get_metric_label(m) for m in self.form_data.get('metrics')],
             aggfunc=self.form_data.get('pandas_aggfunc'),
             margins=self.form_data.get('pivot_margins'),
         )