ci: add instance identifier to backend CI env

Author: candleindark

.github/workflows/backend-ci.yml

@@ -54,6 +54,7 @@ jobs:
       DJANGO_DANDI_API_URL: http://localhost:8000
       DJANGO_DANDI_JUPYTERHUB_URL: https://hub.dandiarchive.org/
       DJANGO_DANDI_INSTANCE_NAME: DANDI
+      DJANGO_DANDI_INSTANCE_IDENTIFIER: "RRID:SCR_017571"
     steps:
       - uses: actions/checkout@v5
       - name: Install uv