Intent of returns_sentinel_when_no_output_exists

All 4 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 4 tests
- server/ 4 tests
  - tools/ 4 tests
    
    testrunner/ 4 tests
    
    TestParseFailureDetails/ 1 test
    
    go.temporal.io/server/tools/testrunner/TestParseFailureDetails/returns_sentinel_when_no_output_exists Introduced here
    
    go.temporal.io/server/tools/testrunner/TestNewSummaryFromReports_KeepsFailureAndAlertRows Inherited TestNewSummaryFromReports_KeepsFailureAndAlertRows
    
    go.temporal.io/server/tools/testrunner/TestRenderSummaryFromReports_JSON Inherited TestRenderSummaryFromReports_JSON
    
    go.temporal.io/server/tools/testrunner/TestRenderSummaryFromReports_Markdown_RendersFailureRows Inherited summary.go ×1