Intent of Test_Check_Serving, edge_case:_mixed_failures_just_under_threshold, +1

All 3 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 3 tests
- server/ 3 tests
  - service/ 3 tests
    
    frontend/ 3 tests
    
    TestHealthCheckerSuite/ 3 tests
    
    Test_Check_Mixed_Host_States_Edge_Cases/ 1 test
    
    go.temporal.io/server/service/frontend/TestHealthCheckerSuite/Test_Check_Mixed_Host_States_Edge_Cases/edge_case:_mixed_failures_just_under_threshold Introduced here
    
    go.temporal.io/server/service/frontend/TestHealthCheckerSuite/Test_Check_Boundary_Failure_Percentage_Equals_Threshold Introduced here
    
    go.temporal.io/server/service/frontend/TestHealthCheckerSuite/Test_Check_Serving Introduced here