Fix fileapi tests

[3coins]

Fixes file api tests, making all unit tests green.

[dlqqq]

It looks like the test_isolated job is failing because it is running on Python 3.9:

     jupyter_server_documents enabled
    - Validating jupyter_server_documents...
       X unsupported operand type(s) for |: 'type' and 'NoneType'

Relates to #74. Zach had mentioned that he would like to avoid Python 3.9 support given that it doesn't support match/case statements used in the backend. I think we can just bump the Python version until we decide to support Python 3.9.

[3coins]

I think we can just bump the Python version until we decide to support Python 3.9

Agree, I will add that change shortly.