I think the action is set to run on push only for the main branch. Otherwise, only PR would run the tests. Deleting these conditions locally in your branch is another option.
to run the test is every branch. The change is not very useful in the main repository, but it would be helpful for people writing PR before they send the PR. Are some of these workflow run automatically weekly or monthly and it would be bad to have too many of them enabled?
Triggering the checks for any branch would mean running the tests twice for every push to every PR. That may have been why @sorawee added the condition.
(FWIW, the push CIs have lots of configurations; the PR checks have much fewer ones.)