BUG: pd.to_datetime doesn't raises AttributeError with specific input…
- [x] closes #12424
- [x] tests added / passed
- [ ] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

…s when errors='ignore'(#12424)

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13909?src=pr) is 85.30% (diff: 100%)

> Merging [#13909](https://codecov.io/gh/pydata/pandas/pull/13909?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #13909   diff @@
==========================================
  Files           139        139          
  Lines         50138      50138          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          42769      42769          
  Misses         7369       7369          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [e5ee5d2...58d3d19](https://codecov.io/gh/pydata/pandas/compare/e5ee5d2e034c9a4be795596633c199d0ba23970b...58d3d196c31b10cb546bc792106bfa79cb71f88b?src=pr)
 pls add a release note as well
 thanks!
