`cut -d: -f2` inside a plain YAML scalar reads as a mapping key, so test-backend.yml was not valid YAML and would have been rejected the first time a runner picked it up. A block scalar takes the whole command as text.
`cut -d: -f2` inside a plain YAML scalar reads as a mapping key, so test-backend.yml was not valid YAML and would have been rejected the first time a runner picked it up. A block scalar takes the whole command as text.