CI_COMMIT_SHA does not allow for `package-and-qa` to run

Summary

package-and-qa passes down CI_COMMIT_SHA which is dynamically generated with after #200037 (closed)

Steps to reproduce

• Create a merge request in gitlab-org/gitlab
• Run package-and-qa
• See error like

 The following shell command exited with status 128:
     $ git -c core.autocrlf=false checkout 6d7224ebf5f9e52f0354f38ce8dcf8fb685bdb97 -f -q
 Output:
     (nothing)
 Error:
     fatal: reference is not a tree: 6d7224ebf5f9e52f0354f38ce8dcf8fb685bdb97

where 6d7224eb is the SHA generated with the pipeline

Potential Fix

Pass down CI_MERGE_REQUEST_SOURCE_BRANCH_SHA instead of CI_COMMIT_SHA for trigger_build