BUG: series resample with timedelta values looses dtype (GH13119)
- [x] closes #13119
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14118?src=pr) is 85.27% (diff: 100%)

> Merging [#14118](https://codecov.io/gh/pydata/pandas/pull/14118?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #14118   diff @@
==========================================
  Files           139        139          
  Lines         50511      50511          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43071      43072     +1   
+ Misses         7440       7439     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [10bf721...c06ac1e](https://codecov.io/gh/pydata/pandas/compare/10bf7213240eaa0960f50f86c7790d64d8973060...c06ac1e09e958dd9bc9ff3ba58a90a1e76154e2c?src=pr)
