Fix CI rules to not run prod jobs when run for a forked repo's MR against the fork's master branch

Chad Woolleyrequested to merge
fix-ci-rules-for-fork-mrs-on-master-branch into master

Why is this change being made?

Fix CI rules to not run prod jobs when run via Pipelines for Merged Results for a forked repo's MR against the fork's master branch.

See internal slack thread

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