CI: PyPy3 testing
- [ ] xref #37653 
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

~~Wow, only 1 failing test here. I guess the crashes/segfaults are probably due to an older numpy then(this needs to be verified though). I guess I'll add more deps in a follow up then.~~
EDIT: This passes w/out deps other than the required ones. I'll add more in follow up thanks @lithomas1 