BUG: Issue with pd.cut on Series with duplicate index
- [x] closes #42185 
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

Creating a new PR. I had messed up the earlier one by mistake.
please review Can you merge master, and fix the problems in the CI please? Ping us when it's green. Thanks! @datapythonista @jreback Green thanks @debnathshoham 