informative comment added

com.unity.perception/Tests/Runtime/GroundTruthTests/LabelEntryMatchCacheTests.cs

 
                 yield return null;
 
+                //this new object has a label that is not included in our label config
                 var labeledPlane2 = TestHelper.CreateLabeledPlane(label: "bar");
                 AddTestObjectForCleanup(labeledPlane2);