executors: fix typing on `compiler_fs`

[Riolku]

We rely on the fs being a list in order to add it to other lists, so we should type it accordingly. MyPy complains about typing in some executors unless they are explicitly typed, see https://mypy.readthedocs.io/en/stable/common_issues.html#variance.

[Riolku]

Converting to draft. MyPy needs to be fixed so this PR can pass CI.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (1806ba4) 82.71% compared to head (12a4fa1) 82.71%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1009   +/-   ##
=======================================
  Coverage   82.71%   82.71%           
=======================================
  Files         141      141           
  Lines        5310     5311    +1     
=======================================
+ Hits         4392     4393    +1     
  Misses        918      918           

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[Riolku]

Converting to draft. MyPy needs to be fixed so this PR can pass CI. See this issue.

[Riolku]

We don't actually rely on these being lists right now... since we don't add them to anything (which is why it typechecks of course), but it's worth adding this for potential future use.

[kiritofeng]

Should we also change https://github.com/DMOJ/judge-server/blob/master/dmoj/cptbox/isolate.py#L45 to List?

[Riolku]

Should we also change https://github.com/DMOJ/judge-server/blob/master/dmoj/cptbox/isolate.py#L45 to List?

Updated.