type-hint fixup

Author: rhshadrach

pandas/core/arrays/string_.py

@@ -904,8 +904,8 @@ def _accumulate(self, name: str, *, skipna: bool = True, **kwargs) -> StringArra
             raise TypeError(msg)
 
         # We may need to strip out trailing NA values
-        tail: np.array | None = None
-        na_mask: np.array | None = None
+        tail: np.ndarray | None = None
+        na_mask: np.ndarray | None = None
         ndarray = self._ndarray
         np_func = {
             "cumsum": np.cumsum,