如何使用python为同一列中包含的相同值设置00:00:00中的时间

import pandas as pd
from datetime import datetime, time

data = {'col1': ['A', 'A', 'B', 'B', 'C', 'C'],
        'col2': ['2022-01-01', '2022-01-02', '2022-01-03', '2022-01-03', '2022-01-04', '2022-01-05']}
df = pd.DataFrame(data)

df['col2'] = pd.to_datetime(df['col2'])

df['col2'] = df.groupby('col1')['col2'].transform(lambda x: x.dt.date)
df['col2'] = pd.to_datetime(df['col2']).dt.time

print(df)

  col1      col2
0    A  00:00:00
1    A  00:00:00
2    B  00:00:00
3    B  00:00:00
4    C  00:00:00
5    C  00:00:00