Switch to using run-tests.sh by default
Problem/Motivation
Using run-tests.sh with concurrency on is *much* faster than not using that.
From @berdir in this slack thread: https://drupal.slack.com/archives/CGKLP028K/p1715113195896199
> on concurrency BC: I get that, but it seems very unlikely that it will break something and it makes tests so much faster, which imho translates directly into how much money DA spends on this. for token module with a fairly limited set of tests, it cut the phpunit job from 3 to 1 minute, for webform, it would be 5m instead of 33min (see https://www.drupal.org/project/webform/issues/3402134#comment-15323262)
As I wrote, I think not a lot of projects should have a problem with this, I never did with all the projects where I enabled it, and my understanding is that it it will also help with D11/PHPUnit 10 compatibility because run-tests.sh abstracts the specific phpunit arguments that are needed away.
If you're worried about BC then one option would be to only do it on next major for now and maybe enable it for all when D11.0 becomes the current minor.
But my personal recommendation is to just switch it. I expect fewer disruptions than for example the cspell job addition which confused quite a few people.
Related issues: Issue #3509614, Issue #2781123, Issue #3374070
Change record: #3620894
Related issue: Issue #3509614
Related issue: Issue #2781123
Related issue: Issue #3374070