CLN: Replace FrameOrSeriesUnion annotation by DataFrame | Series
- [ ] closes #40876 
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry


The FrameOrSeriesUnion check was already removed. I have removed the FrameOrSeriesUnion alias, and replaced all instances of FrameOrSeriesUnion with DataFrame | Series
HI, I have created a new commit. Please review it. Thank you. > HI, I have created a new commit. Please review it. Thank you.

Thanks - can you fetch and merge upstream/master please? Hi @MarcoGorelli, I seem to be stuck. I updated the forked repo on my github page by fetch and merge upstream, and tried to push changes. However, I cannot see the Compare and Pull Request button that usually appears. Initially, I tried force pushing as git would not let me push changes. Thanks.  > I cannot see the Compare and Pull Request button that usually appears

If you've already opened a pull request (as you have), there's no need to open a new one, you can just add a commit and push it Looks like there's a merge conflict, could you resolve it please?

My workflow for doing this would be
```
git fetch upstream
git merge upstream/master
# resolve any conflicts
git commit -a
git push origin
``` Hello @Swanand01! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:















































There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-06-11 17:30:30 UTC