rewrite dict as literal in tests/io/parser/test_index_col.py
for issue # 38138 
rewrite unnecessary dict call as a literal in pandas/tests/io/parser/test_index_col.py

Please let me know if anything needs to be amended, changed or fixed. I'm new to contributing.

- [ ] issue #38138 
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
