fix benchmark result posting

[hakkelt]

In this PR, I try to fix this problem by dividing the benchmarking into two phases:

1. Run the benchmark, save the results to a file, and upload it as an artifact. -> It does not need any special permissions.
2. Download the artifact and post the content as a comment. -> This gets triggered by the first phase via "workflow_run", and my hope is that it is possible to selectively set write permission to this job only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.78%. Comparing base (83c73c9) to head (ab571a6).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #159      +/-   ##
==========================================
- Coverage   94.79%   94.78%   -0.01%     
==========================================
  Files          79       79              
  Lines        2498     2494       -4     
==========================================
- Hits         2368     2364       -4     
  Misses        130      130              

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[hakkelt]

To test this PR, post_benchmark_comment.yml needs to be on master already... So I'll play around a bit in some playground repositories, then I'll report if it works.