There are some jobs where it doesn't make sense to provide an alert of a failure, because they are non voting. For example, mwext-phpunit patch coverage doesn't need a notification:
https://gerrit.wikimedia.org/r/c/mediawiki/extensions/GrowthExperiments/+/889642/31#message-7c9b65493f93ef9f4c260472090346cab394dd0a
Ideally, there is a way to detect via an environment variable that a job is non-voting. In theory ZUUL_VOTING should be that variable, but for mwext-phpunit-coverage-patch-docker it is set to 1, so I am not sure what is going on.
An alternative is to craft a list of jobs that should never trigger notifications.