Use newest helper image version in tests

What does this MR do?

Makes tests use the newest helper image tag that goes alongside the pushed code, instead of latest that is associated with the previous release.

Why was this MR needed?

We can't run integration tests relying on new functionality in the helper image when using the latest tag.

What's the best way to test this MR?

Follow the instructions in docs/development/README.md

What are the relevant issue numbers?

Closes #25652 (closed)