MR patch CI job is not running on targeted branch (example forked out branch like morello/release-1.4 )

There are a MR patche targeted for only forked out branch like morello/release-1.4, it is expected to run the MR patch CI on forked out branch only not on mainline branch. Currently there is no way to specify which MANIFEST_BRANCH should be used in the MR for testing and it defaults to morello/mainline.

Similar issue is observed in MR build-scripts!63 (merged)
This needs to fixed and MR CI should be run against targeted branch only not on the mainline.