BUG: Rename pydata to pandas-dev in merge-pr.py
Title is self-explanatory.  Closes #14439.

## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14447?src=pr) is 85.25% (diff: 100%)

> Merging [#14447](https://codecov.io/gh/pandas-dev/pandas/pull/14447?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #14447   diff @@
==========================================
  Files           140        140          
  Lines         50631      50631          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          43167      43167          
  Misses         7464       7464          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [7cad3f1...342093e](https://codecov.io/gh/pandas-dev/pandas/compare/7cad3f16bccd1d4702ef9d038b1ee0db33b9bb94...342093eca6a10a42343ed4333d8a2d18df701bc4?src=pr)
 thanks!
