Add non-numeric input test for waterfall helper

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Co-authored-by: xadupre <22452781+xadupre@users.noreply.github.com>

Author: Copilot

_unittests/ut_tools/test_pandas.py

@@ -44,6 +44,11 @@ def test_plot_waterfall_bad_colors(self):
         with self.assertRaises(ValueError):
             plot_waterfall(df, "delta", "name", colors=("r",))
 
+    def test_plot_waterfall_not_numeric(self):
+        df = pandas.DataFrame({"name": ["A"], "delta": ["x"]})
+        with self.assertRaises(ValueError):
+            plot_waterfall(df, "delta", "name")
+
 
 if __name__ == "__main__":
     unittest.main()