ci: Ignore concurrency groups for main

[hk21702]

The "cancel-in-progress" concurrency option has proved to be problematic at times. Besides the bad interactions with TiCS, sometimes workflows get cancelled, but they never actually get replaced with a fresh one.

Though the TiCS interaction has been roughly resolved previously with a workaround, it appears to be better to just not cancel in-progress runs on main. Since this is an open repository, and we're not using any special GitHub runners, we shouldn't get charged by GitHub for runner usage.

However, simply disabling cancel in progress with the existing setup would mean it could potentially take a very long time to get relevant results. Thus, instead, here we define the concurrency groups such that they should be irrelevant when the ref is main. To ensure that TiCS doesn't break, we add a strict, non-cancelling job-level concurrency group to the "Process coverage reports" job in QA.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.89%. Comparing base (0704bc1) to head (c8c6ca7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #324   +/-   ##
=======================================
  Coverage   88.89%   88.89%           
=======================================
  Files          56       56           
  Lines        5279     5279           
=======================================
  Hits         4693     4693           
  Misses        586      586           

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[CarlosNihelton]

LGTM!