Skip issuable without a project in IssuableExtractor#extract

Merged username-removed-423915 requested to merge 31280-skip-issueables-without-project into master

This is based on !10894 (closed), instead of checking visibility, we just skip the issuables without a project.

I think it might make more sense to do that in IssueParser and MergeRequestParser, but doing it here might have less impact.

Closes #31280 (closed)