BUG: Add  type check for width parameter in str.pad method GH13598
- [x] closes #13598 
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

Thx! can u add tests all methods uses `str_pad`, i.g. `pad`, `center`, `ljust`, `rjust` and `zfill`.
 I wrote all the tests, however it seemed extremely redundant doing so. I know that redundancy isn't necessarily a bad thing when testing, but is there a better way to implement them?

Thanks
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13690?src=pr) is **84.38%**

> Merging [#13690](https://codecov.io/gh/pydata/pandas/pull/13690?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #13690   diff @@
==========================================
  Files           142        142          
  Lines         51223      51226     +3   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43224      43227     +3   
  Misses         7999       7999          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [ada6bf3...9669f3f](https://codecov.io/gh/pydata/pandas/compare/ada6bf350f7fd4daaf2b80188ca165fb9543a252...9669f3f139445a98d38d7feee1d12ab04fe0362d?src=pr)
 thanks @wcwagner 
