Add missing BASE_PROXY_NAME

Author: stevebux

.github/actions/acceptance-tests/action.yml

@@ -104,6 +104,7 @@ runs:
       run: |
         echo "$SUPPLIER_API_PRIVATE_KEY" > "${GITHUB_WORKSPACE}/internal-dev-test-1.pem"
         chmod 600 "${GITHUB_WORKSPACE}/internal-dev-test-1.pem"
+        BASE_PROXY_NAME=nhs-notify-supplier--internal-dev--nhs-notify-supplier
 
         export API_ENVIRONMENT=internal-dev
         if [[ -z "$PR_NUMBER" ]]; then