Updated source DAG with fallback demo CDCVaccinationNational (#3918)

# Description and Motivation
closes #3783

## Has this been tested? How?

Yes. Using pytest against the file

## Screenshots (if appropriate)

![Screenshot
(151)](https://github.com/user-attachments/assets/fad0ed47-6218-4cba-83c1-435e830fe4a6)

![Screenshot
(152)](https://github.com/user-attachments/assets/6c0df4fe-0939-4c91-9fca-8aebd4070d1a)

## Types of changes

(leave all that apply)

- Refactor / chore

## New frontend preview link is below in the Netlify comment 😎

airflow/dags/cdc_vaccination_national.py

@@ -29,6 +29,7 @@
 
 cdc_vaccination_national_exporter_payload_race = {
     "dataset_name": _CDC_VACCINATION_NATIONAL_DATASET_NAME,
+    "should_export_as_alls": True,
     "demographic": "race",
 }
 cdc_vaccination_national_exporter_operator_race = util.create_exporter_operator(