fix: correct environment variable for Firebase functions deployment

Author: FanyCastro

.github/workflows/firebase-deploy.yml

@@ -44,7 +44,8 @@ jobs:
       - name: Deploy Functions
         run: |
           npm install -g firebase-tools
+          firebase login:ci --token=${FIREBASE_SERVICE_ACCOUNT}
           firebase deploy --only functions
         env:
-          GOOGLE_APPLICATION_CREDENTIALS: "${{ secrets.FIREBASE_SERVICE_ACCOUNT_THINGS_TO_COMPLETE }}"
+          FIREBASE_SERVICE_ACCOUNT: "${{ secrets.FIREBASE_SERVICE_ACCOUNT_THINGS_TO_COMPLETE }}"
           FIREBASE_PROJECT_ID: things-to-complete