Give this a try (but it likely will have no effect)

.drone.yml

@@ -175,6 +175,8 @@ steps:
     path: /var/run/docker.sock
   - name: dockerconfig
     path: /drone/auth/.docker/config.json
+  - name: mongo-init
+    path: /docker-entrypoint-initdb.d/mongo-init.js
 - name: Send Status Notifications
   image: plugins/webhook
   privileged: true
@@ -202,6 +204,8 @@ volumes:
 - name: env-secrets
   host:
     path: /volume1/docker/beethoven/labs-auth/staging.env
+- name: mongo-init
+  path: /drone/auth/mongo-init.js
 
 depends_on:
   - Test Pipeline

mongo-init.js

@@ -1,5 +1,4 @@
 /* eslint-disable no-undef */
-db = db.getSiblingDB(process.env.DB_NAME);
 db.createUser({
     user: process.env.DB_USERNAME,
     pwd: process.env.DB_PASSWORD,