ci: fail the Docker lane if the set-runtime real-owner case is skipped #801

The real-owner case in packages/cli/test/heartbeat-agent-runtime-757.test.ts ("set-runtime keeps the config's group when only the group can be preserved", added in #798) needs root and setpriv, so it is skipped by its prerequisite guard everywhere except the Docker Integration lane. If that lane ever loses either prerequisite, the case skips silently and the lane stays green.

Fix: in the Docker Integration lane only, turn a skip of this case into a failure (for example an environment flag the lane sets, which makes the prerequisite guard fail instead of skip), and keep the skip on hosts without the flag. Pin it by running the lane once with a prerequisite removed and showing it red.