Another regex fix

Author: jessegrabowski

tests/statespace/test_statespace.py

@@ -380,9 +380,12 @@ def test_bad_forecast_arguments(use_datetime_index, caplog):
     time_idx = _make_time_idx(ss_mod, use_datetime_index)
 
     # Start value not in time index
-    with pytest.raises(
-        ValueError, match="Integer start must be in the data index used to fit the model"
-    ):
+    match = (
+        "Datetime start must be in the data index used to fit the model"
+        if use_datetime_index
+        else "Integer start must be within the range of the data index used to fit the model."
+    )
+    with pytest.raises(ValueError, match=match):
         start = time_idx.shift(10)[-1] if use_datetime_index else time_idx[-1] + 11
         ss_mod._validate_forecast_args(time_index=time_idx, start=start, periods=10)