CI: fsspec 2021.6.0 failures
`pandas/tests/io/test_fsspec.py::test_read_csv` and `pandas/tests/io/test_fsspec.py::test_markdown_options` fails with fsspec version 2021.6.0.

Based on the changelog, the culprit might be 
> Better testing and folder handling for Memory (654)

but more investigation needed to see if this is a new bug or something we should fix in the failing tests

Temporary fix in #42023