TST/DOC: apply date() with timezones
- [x] closes #11757
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [ ] whatsnew entry

@rockg Thanks! (added 2 really minor comments)
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14085?src=pr) is 85.26% (diff: 100%)

> Merging [#14085](https://codecov.io/gh/pydata/pandas/pull/14085?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #14085   diff @@
==========================================
  Files           139        139          
  Lines         50492      50492          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43052      43053     +1   
+ Misses         7440       7439     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [5152cdd...394e918](https://codecov.io/gh/pydata/pandas/compare/5152cdd77ba4799a276d2716535255c3301e9741...394e9184c980bba9a4392bef113edf248a836aff?src=pr)
 Thanks!
