Added test of RuntimePropertyCache using properties with different attributes

Author: svick

src/System.Text.Json/tests/Serialization/Object.WriteTests.cs

@@ -77,10 +77,28 @@ public int this[int index]
         }
 
         [Fact]
-        public static void WriteCollectionAsObject()
+        public static void WritePolymorhicSimple()
         {
             string json = JsonSerializer.Serialize(new { Prop = (object)new[] { 0 } });
             Assert.Equal(@"{""Prop"":[0]}", json);
         }
+
+        [Fact]
+        public static void WritePolymorphicDifferentAttributes()
+        {
+            string json = JsonSerializer.Serialize(new Polymorphic());
+            Assert.Equal(@"{""P1"":"""",""p_3"":""""}", json);
+        }
+
+        private class Polymorphic
+        {
+            public object P1 => "";
+
+            [JsonIgnore]
+            public object P2 => "";
+
+            [JsonPropertyName("p_3")]
+            public object P3 => "";
+        }
     }
 }