Revert "CI: runtime warning in npdev build (pandas-dev#42413)" (pandas-dev#42539)

This reverts commit a69603d.

Author: lithomas1

pandas/tests/scalar/timedelta/test_arithmetic.py

@@ -18,6 +18,7 @@
     NaT,
     Timedelta,
     Timestamp,
+    compat,
     offsets,
 )
 import pandas._testing as tm
@@ -437,7 +438,7 @@ def test_td_div_numeric_scalar(self):
                 np.float64("NaN"),
                 marks=pytest.mark.xfail(
                     # Works on numpy dev only in python 3.9
-                    is_numpy_dev,
+                    is_numpy_dev and not compat.PY39,
                     raises=RuntimeWarning,
                     reason="https://github.com/pandas-dev/pandas/issues/31992",
                 ),