DOC: Fix EX02 and SA01 in DataFrame.select_dtypes
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Related to #27977. 

output of `python scripts/validate_docstrings.py pandas.DataFrame.select_dtypes`:
```
################################################################################
################################## Validation ##################################
################################################################################

1 Errors found:
        No extended summary found
```

Notes:
It seems like passing `int` to the parameter do not include/exclude all integer dtypes. But, passing `integer` would do otherwise. I think it is related to this issue https://github.com/pandas-dev/pandas/issues/29394. It would be more convenient if passing `int` as an input would match the result with passing `integer`.

