Add a git tag in the related branches service spec

What does this MR do and why?

Add a git tag in the related branches service spec. This asserts that tags are not returned when searching for related branches.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #367746 (closed)