Fixed netfx System.ComponentModel.DataAnnotations.Tests.ValidatorTests.TryValidateObject_RequiredNull_Error on non English Windows (#28148)

Author: AlexRadch

src/System.ComponentModel.Annotations/tests/ValidatorTests.cs

@@ -229,7 +229,7 @@ public void TryValidateObject_RequiredNull_Error()
 
             var results = new List<ValidationResult>();
             Assert.False(Validator.TryValidateObject(instance, context, results));
-            Assert.Equal("The Required field is required.", Assert.Single(results).ErrorMessage);
+            Assert.Contains("Required", Assert.Single(results).ErrorMessage);
         }
 
         public class RequiredFailure