TST (string dtype): follow-up fix for pyarrow 19.0 update
Small follow-up on https://github.com/pandas-dev/pandas/pull/60716. This change is already included in the backport PR https://github.com/pandas-dev/pandas/pull/60755, so targeting 3.0 here (on 2.3.x this was needed because there for some reason more jobs were already using pyarrow 19.0)
```bash
=========================== short test summary info ============================
FAILED pandas/tests/io/test_parquet.py::TestBasic::test_parquet_read_from_url[pyarrow] - AssertionError: DataFrame.columns are different

Attribute "dtype" are different
[left]:  object
[right]: StringDtype(storage=pyarrow, na_value=nan)
``` Thanks @jorisvandenbossche 