If your testing is time consuming to the point that you can only test on your PRs and never on what master would be after each one merges, then you have to choo

If your testing is time consuming to the point that you can only test on your PRs and never on what master would be after each one merges, then you have to choose between somehow forcing PR authors to serialize their merges somehow (external convention or tooling or something) or not testing the code that will actually be released. The latter isn’t always the wrong choice, though.