Fix feature branch commit encoded into the artifacts' names (fixes: #18468)
Since !381 (merged) (Merge base branch earlier) or some of its follow-ups we've encoded the merge-commit as the feature branch's commit. This is a problem since this commit often (and always on Jenkins) is throw-away and thus not visible outside of the Git repo it was made in, making this information useless. So let's encode the commit prior to the base branch merge.
Closes #18468 (closed)