Add tests for service name empty
What
Add test to check when service is empty in Docker executor.
Why
In !5063 (merged) we updated the error to be a build error where before it was a system failure.
Reference: #38234 (closed)
Testing
$ go test -v -run TestDockerCommandServiceNameEmpty -tags integration ./executors/docker
time="2024-10-10T08:25:48+02:00" level=info msg="Created missing unique system ID" system_id=s_440cc01f651a
=== RUN TestDockerCommandServiceNameEmpty
=== RUN TestDockerCommandServiceNameEmpty/bridge_network
=== RUN TestDockerCommandServiceNameEmpty/network_per_build
--- PASS: TestDockerCommandServiceNameEmpty (2.54s)
--- PASS: TestDockerCommandServiceNameEmpty/bridge_network (0.60s)
--- PASS: TestDockerCommandServiceNameEmpty/network_per_build (1.37s)
PASS
ok gitlab.com/gitlab-org/gitlab-runner/executors/docker 3.320s