Fix cache service coverage for Minion tasks

[kraih]

#4526 showed that coverage is not collected correctly for Minion tasks.

[codecov]

Codecov Report

Merging #4532 (43127a4) into master (4c3e524) will increase coverage by 0.00%.
The diff coverage is 94.11%.

❗ Current head 43127a4 differs from pull request most recent head fb7ce43. Consider uploading reports for the commit fb7ce43 to get more accurate results

@@           Coverage Diff           @@
##           master    #4532   +/-   ##
=======================================
  Coverage   97.97%   97.97%           
=======================================
  Files         374      375    +1     
  Lines       34108    34126   +18     
=======================================
+ Hits        33416    33435   +19     
+ Misses        692      691    -1     

Impacted Files	Coverage Δ
t/lib/OpenQA/Test/Utils.pm	83.76% <88.88%> (+1.49%)	⬆️
lib/OpenQA/CacheService.pm	100.00% <100.00%> (ø)
script/openqa-workercache	100.00% <100.00%> (ø)
lib/OpenQA/CacheService/Command/run.pm	66.66% <0.00%> (ø)

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[kraih]

Even after a few iterations, it does not look like the change had the effect i was hoping for. Back to the drawing board i guess.

[kraih]

I know the current code is wrong, but i can't prove it with tests yet.