BUG: not correct work str.split
### 

- [ ] I have checked that this issue has not already been reported.

- [ ] I have confirmed this bug exists on the [latest version](https://pandas.pydata.org/docs/whatsnew/index.html) of pandas.

- [X] I have confirmed this bug exists on the master branch of pandas.


### Reproducible Example

```python
import pandas as pd

df = pd.DataFrame(columns=['url'])
df['url'] = ['https://qweqwe.com/2021-09-14/qweqwejpgqweqwe.jpg']
df['id'] = df['url'].str.split('/').str[-2].astype(str) + '_' + df['url'].str.split('/').str[-1].str.split('.jpg').str[0]
print(df['id'].iloc[0])
```


### Issue Description

output: 2021-09-14_qweqw
true output: 2021-09-14_qweqwejpgqweqwe

### Expected Behavior

2021-09-14_qweqwejpgqweqwe

### Installed Versions

python 3.9
pandas version 1.3.2