Support merged results from main-jh for corresponding JH branch for as-if-jh pipeline
This was discovered at !99479 (comment 1218805956)
Where if it's running merged results pipeline, the validation pipeline should pass. For now it's using the branch directly which we have to rebase in order to get fixes from the default branch (main-jh
in this case)
We should also consider #387840 so that we're running an actual merge request pipeline, to be more efficient.
Edited by Lin Jen-Shin