compile-test-assets as-if-jh fails for 14.4 backports

The compile-test-assets as-if-jh job is failing in 14-4-stable-ee: https://gitlab.com/gitlab-org/security/gitlab/-/jobs/1799215651 and https://gitlab.com/gitlab-org/security/gitlab/-/jobs/1799588932 are two examples.

This will block the security release as all 14.4 backports have failing pipelines.

On Slack, @engwan suggested:

Looks like it’s pulling the Gemfile from master? Maybe we shouldn’t run this job on old branches?

If we don't do that, we at least need a backport for !74107 (merged).