fix minor issues

Author: aaronchucarroll

pandas/core/strings/accessor.py

@@ -2482,9 +2482,11 @@ def get_dummies(
         1   False  False   False
         2   True   False   True
         """
+        from pandas.core.dtypes.common import is_string_dtype
+
         from pandas.core.frame import DataFrame
 
-        if dtype in (str, "str[pyarrow]"):
+        if is_string_dtype(dtype):
             raise ValueError("string dtype not supported, please use a numeric dtype")
         # we need to cast to Series of strings as only that has all
         # methods available for making the dummies...

pandas/tests/strings/test_get_dummies.py

@@ -11,11 +11,6 @@
     _testing as tm,
 )
 
-try:
-    import pyarrow as pa
-except ImportError:
-    pa = None
-
 
 def test_get_dummies(any_string_dtype):
     s = Series(["a|b", "a|c", np.nan], dtype=any_string_dtype)