REF: "bare_pytest_raises" to use the ast module
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

---

There is also a performance boost:

```
In [1]: import os                                                                                             

In [2]: from scripts.validate_unwanted_patterns import bare_pytest_raises, main                               

In [3]: SOURCE_PATH = "pandas/tests/"                                                                         

In [4]: %timeit main(function=bare_pytest_raises, source_path=SOURCE_PATH, output_format="{source_path}:{line_number}:{msg}.") 

12.6 s ± 76.4 ms per loop (mean ± std. dev. of 7 runs, 1 loop each) # Master
4.33 s ± 27 ms per loop (mean ± std. dev. of 7 runs, 1 loop each) # PR
```