Remove Python 3.8 support

[g-as]

No description provided.

[cosmicBboy]

the ci error looks odd:

ImportError while loading conftest '/home/runner/work/pandera/pandera/tests/core/conftest.py'.
tests/core/conftest.py:4: in <module>
    from tests.core.checks_fixtures import (
tests/core/checks_fixtures.py:9: in <module>
    import pandera as pa
pandera/__init__.py:26: in <module>
    from pandera.api.pandas.array import SeriesSchema
pandera/api/pandas/array.py:15: in <module>
    from pandera.engines import pandas_engine
pandera/engines/pandas_engine.py:1216: in <module>
    class PydanticModel(DataType):
pandera/engines/pandas_engine.py:1219: in PydanticModel
    type: type[BaseModel] = dataclasses.field(default=None, init=False)  # type: ignore[assignment]
E   TypeError: 'Field' object is not subscriptable