use np.issubdtype instead of is_string_dtype

Author: 5j9

pandas/core/dtypes/cast.py

@@ -1851,7 +1851,7 @@ def maybe_cast_to_integer_array(
     # doesn't handle `uint64` correctly.
     arr = np.asarray(arr)
 
-    if is_string_dtype(arr):
+    if np.issubdtype(arr.dtype, str):
         return casted
 
     if is_unsigned_integer_dtype(dtype) and (arr < 0).any():