Fix TokenObtainPairSerializer to declare access and refresh fields for schema accuracy

- Explicitly declare 'access' and 'refresh' fields as read-only
- Ensures schema generators (drf-yasg, DRF core) reflect the actual response
- No runtime behavior change

Author: pre-commit-ci[bot]

tests/test_serializers.py

@@ -217,13 +217,14 @@ def test_schema_fields_do_not_break_runtime_validation(self):
         # Tokens should be valid
         access_token = AccessToken(validated_data["access"])
         refresh_token = RefreshToken(validated_data["refresh"])
-        
+
         # Validate token type and some claims, but don't assert JTI equality
         self.assertEqual(access_token["token_type"], "access")
         self.assertEqual(refresh_token["token_type"], "refresh")
         self.assertEqual(access_token["user_id"], str(self.user.id))
         self.assertEqual(refresh_token["user_id"], str(self.user.id))
 
+
 class TestTokenRefreshSlidingSerializer(TestCase):
     def setUp(self):
         self.username = "test_user"