BLD: minor break ci/requirements-optional-pip.txt
- [x] closes #22595 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

When adding optional dependencies, below error appears from 

> Invalid requirement: 'openpyxl=2.5.5'
> = is not a valid operator. Did you mean == ?

To core dev, should we fix the version or simply specify lower bound (i.e. >=)?