Bug 1784179 - Don't stop at the first error during CI builds. r=firefox-build-system-reviewers,nalexander

It can be a frustrating experience to push something to e.g. try, get
build errors, fix them, and realize on a subsequent push that there were
other build errors, but since the build failed as soon as it reached the
first error, the logs didn't show them.

While stopping at the first error locally is more helpful locally
(although it still stop immediately and errors are often buried in the
logs), it is actually desirable to avoid stopping on automation.

Differential Revision: https://phabricator.services.mozilla.com/D154327