Use pipeline helper-binary for custom, instance and ssh integration tests

What does this MR do?

For some executors, the helper binary "gitlab-runner" used is the local helper binary already installed in the build environment, and not a helper binary built from sources in the pipeline.

This makes a change for the custom, instance and ssh integration tests to do what the shell executor does, which is to build a helper binary for that executor to use.

Why was this MR needed?

Tests should consistently use a helper binary that's built from the current sources.

What's the best way to test this MR?

Pipeline should pass.

What are the relevant issue numbers?

Closes #38634 (closed)