Added str to index_col attribute in the read_excel function description
- [ ] closes #55843
- [ ] All [code checks passed]
- [ ] Added [type annotations] to new arguments/methods/functions.

@shyamala-venkat - thanks for the PR, I edited your OP above so that the issue reads `#55843`. By including the `#`, GitHub links to the issue and it will automatically be closed when this PR is merged.
 Thanks @shyamala-venkat  Thank you @rhshadrach for approving the pull request.