Add rule for project-update-bot to test against next major
Problem/Motivation
Project update bot creates MRs for projects. These should also be tested against Next Major even if OPT_IN_TEST_NEXT_MAJOR is not turned on
Steps to reproduce
Proposed resolution
Modify the rule that runs against next major when source branch is "project-update-bot-only" which is currectly a static branch that the update bot runs against.