Lower the number of parallel builds on s390x

Given that we have 5 s390x VM instances, each configured with 8vCPU's, we need to consider lowering the number of parallel builds on each VM from 3 to 1.

The builds are running Make with a parallel of 7 thus the 1 build per VM.
This can be achieved by updating the global lock file in worker_locks.yaml

Queues might grow a bit but at the same time having proper CPU -> build allocation will make builds faster and much more stable (minimize chances of timeouts during packaging or unstable MTR tests which are sensible on time).