Follow up on behavior difference in `NullableAnalysis_24_State_From_NotType_Test_Class` and `NullableAnalysis_27_State_From_NotValue_Test_Class` unit-tests in `UnionsTests.cs`

Note a difference in diagnostics reported for Unions scenario and equivalent non-Unions scenario. Behavior for Unions scenario looks expected. The question is why do we get different behavior for non-Union scenario?