CI: Unpin fsspec
- [ ] closes #42026
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

Testing a change out to see if it fixes it. Not sure if this is a bug on our side our on fsspec side. 

It seems the change is that fastparquet apends a slash in front of paths now.

cc @martindurant 
thanks @lithomas1 prob not worth to backport this.