Update stable branch check tooling

What does this MR do and why?

This backports !137316 (merged) to 16-6-stable-ee to ensure pipelines are not blocked by Danger.

There are multiple e2e:package-and-test pipelines, including follow-up-e2e:package-and-test-ee. This MR updates the stable branch tooling logic to search for an exact match to prevent false positives in Danger.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.