Intent of list_workers_from_empty_namespace, list_workers_from_non-existent_namespace

All 2 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 2 tests
- server/ 2 tests
  - service/ 2 tests
    
    matching/ 2 tests
    
    workers/ 2 tests
    
    TestRegistryImpl_ListWorkers/ 2 tests
    
    go.temporal.io/server/service/matching/workers/TestRegistryImpl_ListWorkers/list_workers_from_empty_namespace Introduced here
    
    go.temporal.io/server/service/matching/workers/TestRegistryImpl_ListWorkers/list_workers_from_non-existent_namespace Introduced here