STYLE pylint: 48855-duplicate-value
Issue #48855. This PR enables pylint type "W" warning: `duplicate-value`
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
apologies, this was an accident, I swapped back to the wrong tab, I meant to merge https://github.com/pandas-dev/pandas/pull/49527, looks like this one's failing one check
```
pylint..................................................................................................Failed
- hook id: pylint
- exit code: 8

************* Module pandas.core.dtypes.concat
pandas/core/dtypes/concat.py:284:8: R1720: Unnecessary "elif" after "raise", remove the leading "el" from "elif" (no-else-raise)

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Your code has been rated at 10.00/10
``` Hi @MarcoGorelli , my local pylint passes. I don’t know if this error is related to my changes. Could you please show me how the fixup for R1720 https://github.com/pandas-dev/pandas/pull/49537/commits/9739c1da8f4794f76f6f9280927962a31e583169 relates to this PR?

 Hey @natmokval - you're right, it didn't come from your PR, it came from https://github.com/pandas-dev/pandas/pull/49520 , but that check was failing in this PR's CI, so I should've waited to fix that one first before merging this one

Thanks for all your help fixing these linting issues! Thank you @MarcoGorelli for the explanation. It helps me to understand how changes are getting in.