type hint fixes for adaptive/learner/skopt_learner.py

Author: basnijholt

adaptive/learner/skopt_learner.py

@@ -63,9 +63,7 @@ def ask(
         self, n: int, tell_pending: bool = True
     ) -> Union[
         Tuple[List[float], List[float]],
-        Tuple[List[List[float]], List[float]],
-        Tuple[List[List[float]], List[float]],
-        Tuple[List[float], List[float]],
+        Tuple[List[List[float]], List[float]],  # XXX: this indicates a bug!
     ]:
         if not tell_pending:
             raise NotImplementedError(