[BUG] Correct path to cache for cleanup of task download failure

[PGijsbers]

Fixes an issue that I believe was introduced in #1584: the function called already generates the directory that is task specific, so there is no need to check for a subdirectory. I believe that this patch achieves the intended behavior change of #1584. The corresponding unit test now passes (tests/test_tasks/test_task_functions.py::test_removal_upon_download_failure), where it would previously fail since the subdirectory was never made.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.74%. Comparing base (99928f8) to head (83e1531).

Files with missing lines	Patch %	Lines
openml/tasks/functions.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1620      +/-   ##
==========================================
- Coverage   52.75%   52.74%   -0.02%     
==========================================
  Files          36       36              
  Lines        4333     4332       -1     
==========================================
- Hits         2286     2285       -1     
  Misses       2047     2047              

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