As it was discussed in bitcoin/bitcoin#22980:
seeing all of the failed tests can give us a useful hint for debugging (was thinking about that while reviewing and testing bitcoin/bitcoin#23300).
There is a concern about such approach:
If there is a CI failure, it will be good to know the result as early as possible after opening the pull request.
But, OTOH:
the average amount of saved time for such an approach [using
--failfast] is less significant than it could appear.