AWS: Properly handle requests to list the file system

[MrSerth]

AWS won't support listing the file system. However, since CodeOcean calls the method for each runner, this would yield an error every time. We want to avoid these errors and hence just handle this more gracefully.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.24%. Comparing base (1af6fcc) to head (cef4858).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/api/runners.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #698      +/-   ##
==========================================
- Coverage   76.30%   76.24%   -0.06%     
==========================================
  Files          43       43              
  Lines        3688     3688              
==========================================
- Hits         2814     2812       -2     
- Misses        638      640       +2     
  Partials      236      236              

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