TST: add test for mixed dtypes of df col index #47382
- [x] closes #47382
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

Modified the code snippet reproducing the error into a test under tests/frame/test_arithmetic.py.
Thanks @mliu08 