read_excel() modifies provided types dict when accessing file with duplicate column
- [x] closes #42462
- [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
- [ ] whatsnew entry

The dict is being changed below. Preventing this will require a bigger change.

https://github.com/pandas-dev/pandas/blob/3c10f1f7da63f47d086b127c47fe9aca215d98e1/pandas/io/parsers/python_parser.py#L428-L434 This was introduced in #41411. You can try changing the modified Code there to avoid this and you can use the Tests I have added there  please review HI @phofl @jreback @mzeitlin11 - do you mind taking a look, if this is okay now? I‘ll have a look shortly  Hi @jreback @phofl could you pls take a look, if this is fine? Lets do this for 1.3.2, was a regression  Hello @debnathshoham! 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 2021-08-04 14:23:43 UTC I have added the whatsnew entry in 1.3.2 as @phofl suggested.
@jreback Greenish (unrelated failures).  thanks @debnathshoham  @meeseeksdev backport 1.3.x Something went wrong ... Please have  a look at my logs.