Fix synchronising stable branches upon pushing commits

What does this MR do?

This fixes the CI config used for syncing branches to gitlab-foss and the security mirror. This was broken due to the changes introduced in !24616 (merged) and !25150 (merged). This MR also adds the Delivery team as a code owner of the CI file so we can review changes made to this file.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content