fix: update environment variable for Firebase deployment

Author: FanyCastro

.github/workflows/firebase-deploy.yml

@@ -46,5 +46,5 @@ jobs:
           npm install -g firebase-tools
           firebase deploy --only functions
         env:
-          FIREBASE_TOKEN: "${{ secrets.FIREBASE_SERVICE_ACCOUNT_THINGS_TO_COMPLETE }}"
+          GOOGLE_APPLICATION_CREDENTIALS: "${{ secrets.FIREBASE_SERVICE_ACCOUNT_THINGS_TO_COMPLETE }}"
           FIREBASE_PROJECT_ID: things-to-complete