support numpy 2.0 string

Author: jorisvandenbossche

pandas/core/arrays/string_.py

@@ -292,7 +292,7 @@ def _get_common_dtype(self, dtypes: list[DtypeObj]) -> DtypeObj | None:
             if isinstance(dtype, StringDtype):
                 storages.add(dtype.storage)
                 na_values.add(dtype.na_value)
-            elif isinstance(dtype, np.dtype) and dtype.kind == "U":
+            elif isinstance(dtype, np.dtype) and dtype.kind in ("U", "T"):
                 continue
             else:
                 return None

pandas/tests/arrays/string_/test_concat.py

@@ -7,6 +7,7 @@
 
 import pandas as pd
 import pandas._testing as tm
+from pandas.util.version import Version
 
 
 @pytest.mark.parametrize(
@@ -66,3 +67,7 @@ def test_concat_with_numpy(string_dtype_arguments):
     # with any other numpy dtype -> object
     assert find_common_type([dtype, np.dtype("S")]) == np.dtype("object")
     assert find_common_type([dtype, np.dtype("int64")]) == np.dtype("object")
+
+    if Version(np.__version__) >= Version("2"):
+        assert find_common_type([dtype, np.dtypes.StringDtype()]) == dtype
+        assert find_common_type([np.dtypes.StringDtype(), dtype]) == dtype