BUG: Respect errors="ignore" during extension astype
- [x] closes https://github.com/pandas-dev/pandas/issues/35471
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @dsaxton! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:







There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-09-06 00:58:13 UTC thanks @dsaxton  @meeseeksdev backport 1.1.x