Move utility to private (nunit#4767)

src/NUnitFramework/framework/TestContext.cs

@@ -519,7 +519,7 @@ public IDictionary<PropertyHierachyItem, IList> PropertyHierarchy()
             /// The returned values include the name of the level they are found at.
             /// </summary>
             /// <returns></returns>
-            public IList<PropertyValueHierarchyItem> PropertyValues(string property)
+            private IList<PropertyValueHierarchyItem> PropertyValues(string property)
             {
                 var values = new List<PropertyValueHierarchyItem>();
                 ITest? test = _test;