[MNT] pandas 2.2.X compatibility fixes (#5840)

Adds fixes for `pandas 2.2.X` compatibility:

* ensures index sorting in `update_predict` - previously, this was
automatic, but now has to be enforced due to behaviour change of
`pd.concat`.

sktime/forecasting/base/_base.py

@@ -2511,4 +2511,9 @@ def _format_moving_cutoff_predictions(y_preds, cutoffs):
         cutoffs = [cutoff[0] for cutoff in cutoffs]
         y_pred = pd.concat(y_preds, axis=1, keys=cutoffs)
 
+    if not y_pred.index.is_monotonic_increasing:
+        y_pred = y_pred.sort_index()
+    if hasattr(y_pred, "columns") and not y_pred.columns.is_monotonic_increasing:
+        y_pred = y_pred.sort_index(axis=1)
+
     return y_pred