HHH-18712 Warning about attempts to update an immutable entity for normal (not immutable) entity

tooling/metamodel-generator/src/main/java/org/hibernate/processor/validation/MockEntityPersister.java

@@ -223,4 +223,9 @@ public abstract class MockEntityPersister implements EntityPersister, Joinable,
 	public Type getDiscriminatorType() {
 		return factory.getTypeConfiguration().getBasicTypeForJavaType(String.class);
 	}
+
+	@Override
+	public boolean isMutable() {
+		return true;
+	}
 }