Groupby field does not get serialized.

[baasman92]

Describe the bug
A clear and concise description of what the bug is.

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of pandera.
• (optional) I have confirmed this bug exists on the main branch of pandera.

You can follow the following snippet to reproduce the error:

Code Sample, a copy-pastable example

import pandera as pa
import pandera.extensions as extensions
import pandas as pd

from typing import Dict


@extensions.register_check_method(
    statistics=["group_a", "group_b"],
    check_type="groupby",
)
def groupby_check(dict_groups: Dict[str, pd.Series], *, group_a, group_b):
    return dict_groups[group_a].mean() > dict_groups[group_b].mean()


data = pd.DataFrame(
    {
        "values": [20, 10, 1, 15],
        "groups": list("xxyy"),
    }
)

schema = pa.DataFrameSchema(
    {
        "values": pa.Column(
            int,
            pa.Check.groupby_check(group_a="x", group_b="y", groupby="groups"),
        ),
        "groups": pa.Column(str),
    }
)

schema.to_yaml("/tmp/schema.yml")

serialized_schema = pa.DataFrameSchema.from_yaml("/tmp/schema.yml")

serialized_schema.validate(data)

Expected behavior

I would expect the dict_groups to be passed to the groupby_check function, but instead the entire series is passed without the groupby.

Desktop (please complete the following information):

• Centos 7
• Pandera version: 0.20.4
• Python version: 3.10.9