Enable auth emulator integration tests in CI

Author: muru

.github/workflows/ci.yml

@@ -30,6 +30,8 @@ jobs:
       run: |
         npm install -g firebase-tools
         firebase emulators:exec --only database --project fake-project-id 'pytest integration/test_db.py'
+        echo mock-api-key > apikey.txt
+        firebase emulators:exec --only auth --project mock-project-id 'pytest integration/test_auth.py --cert tests/data/service_account.json --apikey apikey.txt'
 
   lint:
     runs-on: ubuntu-latest