Continuous Integration: Add Codecov settings

[priethor]

What

Adds Codecov settings.

Why

To tune the code coverage part of CI and adapt it to SCF. In particular, the current coverage is still low and it's likely that backport PRs will lower the coverage in a high proportion, so we shouldn't block those PRs, code coverage should be informative.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 1.17%. Comparing base (41a727c) to head (f99e491).
⚠️ Report is 1 commits behind head on trunk.

Additional details and impacted files

@@           Coverage Diff           @@
##             trunk    #233   +/-   ##
=======================================
  Coverage     1.17%   1.17%           
  Complexity    4416    4416           
=======================================
  Files          261     261           
  Lines        27017   27017           
=======================================
  Hits           318     318           
  Misses       26699   26699           

☔ View full report in Codecov by Sentry.
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[github-actions]

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Props priethor.

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