Make sure continuous integration triggers on PR created from forks

[acelaya]

Update the continuous integration workflow so that it triggers when pushing to main branch, but also when creating a pull request.

So far we were running it only when pushing to any branch, which was fine for PRs created directly from this repository.

However, if a PR was created from a fork, continuous integration would not trigger. Now it should.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (8f08381) to head (930b699).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1807   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           68        68           
  Lines         1234      1234           
  Branches       468       468           
=========================================
  Hits          1234      1234           

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