HHH-18382 Fix embeddable disc-formula insertable / updatable flags

Author: mbellade

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/EmbeddableMappingTypeImpl.java

@@ -766,8 +766,8 @@ private EmbeddableDiscriminatorMapping generateDiscriminatorMapping(
 				bootDescriptor.getTable().getName(),
 				discriminatorColumnExpression,
 				isFormula,
-				true,
-				true,
+				!isFormula,
+				!isFormula,
 				columnDefinition,
 				selectable.getCustomReadExpression(),
 				length,