BUG: Fix to_datetime() cache behaviour to not omit duplicated output values
- [x] closes #42259 
- [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

Added a note
 thanks @zyc09  @meeseeksdev backport 1.3.x