Coverage artifacts should be optional for as-if-foss

What does this MR do and why?

Coverage artifacts should be optional for as-if-foss

We might not be running all RSpec jobs therefore some artifact collectors won't be available. This aligns with other artifact collectors.

However, needs.optional is not available when cross project pipeline is involved. To work around this, always let the collectors run for the as-if-foss pipeline. All artifacts are optional so this should be fine.

This fixes https://gitlab.com/gitlab-org/gitlab/-/jobs/6067324148

How to validate

Tested at: !143490 (closed) which is a merge request based on this merge request picking !143128 (merged) where it's reproduced. The as-if-foss pipeline does have all the 3 required collectors: https://gitlab.com/gitlab-org/gitlab-foss/-/pipelines/1160347019