chore[ci]: upload code coverage once

[tserg]

What I did

Consolidate code coverage files and upload it once.

How I did it

How to verify it

Commit message

``
chore[ci]: upload code coverage once

This commit updates the CI to append code coverage to a
single file and make a single upload at the end of all test
runs.

### Description for the changelog

### Cute Animal Picture

![Put a link to a cute animal picture inside the parenthesis-->](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRgJ3cioNlT_vjx1iffqo3KrCBWwys_hC-D9w&s)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.00%. Comparing base (c208b95) to head (3c286ed).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4452      +/-   ##
==========================================
- Coverage   92.01%   92.00%   -0.02%     
==========================================
  Files         119      119              
  Lines       16692    16692              
  Branches     2805     2805              
==========================================
- Hits        15359    15357       -2     
- Misses        915      917       +2     
  Partials      418      418              

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[tserg]

I haven't been able to figure this out. In order to do coverage combine, we need the raw .coverage data file to be unique per run. This would require the parallel flag in coverage to be set to be true. Since the pytest-cov plugin overrides the parallel flag, we need to rely on the coverage package directly. However, there is still an issue of combining duplicate data - I tried doing combine for the fuzzing run only but it gives the same error.