Type of Request

infra task

Infrastructure Environment

LUCI + Cocoon? Not 100% sure.

What is happening?

In #144835, @gaaclarke and I plan to run a "mock" release of flutter/engine, for the first time with golden-file tests enabled, and test out our proposed workflow.

Steps to reproduce

N/A

Expected results

I think I need infra support:

1. What process should I follow to create a "mock" release branch?
2. How can I enable golden-file tests/GOLDCTL for this branch (it's disabled today IIRC)

/cc @zanderso