Add missing type for TestCase.captureOnCommitCallbacks (#1016)

* add missing type for TestCase.captureOnCommitCallbacks

* change default value

django-stubs/test/testcases.pyi

@@ -183,6 +183,7 @@ class TransactionTestCase(SimpleTestCase):
 class TestCase(TransactionTestCase):
     @classmethod
     def setUpTestData(cls) -> None: ...
+    def captureOnCommitCallbacks(cls, *, using: Optional[str] = ..., execute: bool = ...): ...
 
 class CheckCondition:
     conditions: Sequence[Tuple[Callable, str]] = ...