[5.0.x] Added missing skips in constraint tests.

Backport of b6ad8b6 from main.

Author: timgraham

tests/constraints/tests.py

@@ -865,6 +865,7 @@ def test_validate(self):
                 ChildUniqueConstraintProduct(name=self.p1.name, color=self.p1.color),
             )
 
+    @skipUnlessDBFeature("supports_table_check_constraints")
     def test_validate_fields_unattached(self):
         Product.objects.create(price=42)
         constraint = models.UniqueConstraint(fields=["price"], name="uniq_prices")
@@ -1039,6 +1040,7 @@ def test_validate_nullable_textfield_with_isnull_true(self):
         is_not_null_constraint.validate(Product, Product(price=4, discounted_price=3))
         is_not_null_constraint.validate(Product, Product(price=2, discounted_price=1))
 
+    @skipUnlessDBFeature("supports_table_check_constraints")
     def test_validate_nulls_distinct_expressions(self):
         Product.objects.create(price=42)
         constraint = models.UniqueConstraint(