fix(admin): exit dev test queue producer loop when context is cancelled

[Kadajett]

The dev-mode test queue producer goroutine's select had an empty <-ctx.Done() case with no return. Once the context is cancelled, that case is permanently ready, so the loop busy-spins and allocates a new time.After timer on every iteration instead of exiting. Add the missing return so the goroutine stops on shutdown.

[Kadajett]

Also Hi! This is my first contribution! I am just going on a bug hunt on OSS that my friends recommend!

This is the only one that caught my eye initially, as someone who doesn't know the software super well yet!

Its a slam dunk, but on one of those child-sized basketball nets lol