Google App Engine GitHub Action: Error: Unexpected token � in JSON at position 0

Question

I'm trying to deploy my Django API on to Google App Engine using GitHub CI/CD, but I'm getting a strange error that doesn't provide any stack trace in my deploy job. My build job with unit tests and code coverage passes.

main.yaml:

name: Python application

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

defaults:
  run:
    working-directory: src

jobs:
  build:

    runs-on: ubuntu-latest

    services:
      postgres:
        image: postgres:10.8
        env:
          POSTGRES_USER: postgres
          POSTGRES_PASSWORD: postgres
          POSTGRES_DB: github_actions

        ports:
          - 5433:5432

        options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5

    steps:
    - uses: actions/checkout@v2
    - name: Set up Python 3.9
      uses: actions/setup-python@v2
      with:
        python-version: 3.9
    - name: Install dependencies
      run: |
        python -m pip install --upgrade pip
        pip install -r requirements.txt
    - name: Test with Unittest
      env:
        SECRET_KEY: ${{ secrets.SECRET_KEY }}
        DB_NAME: ${{ secrets.DB_NAME }}
        DB_USER: ${{ secrets.DB_USER }}
        DB_PASSWORD: ${{ secrets.DB_PASSWORD }}
        DB_HOST: ${{ secrets.DB_HOST }}
        DB_PORT: ${{ secrets.DB_PORT }}
        DB_ENGINE: ${{ secrets.DB_ENGINE }}
      run: |
        coverage run manage.py test && coverage report --fail-under=75 && coverage xml
        mv coverage.xml ../
    - name: Report coverage to Codecov
      env:
        SECRET_KEY: ${{ secrets.SECRET_KEY }}
        DB_NAME: ${{ secrets.DB_NAME }}
        DB_USER: ${{ secrets.DB_USER }}
        DB_PASSWORD: ${{ secrets.DB_PASSWORD }}
        DB_HOST: ${{ secrets.DB_HOST }}
        DB_PORT: ${{ secrets.DB_PORT }}
        DB_ENGINE: ${{ secrets.DB_ENGINE }}
      uses: codecov/codecov-action@v1
      with:
        token: ${{ secrets.CODECOV_TOKEN }}
        files: ./coverage.xml
        directory: ./coverage/reports/
        fail_ci_if_error: true

  deploy:

    runs-on: ubuntu-latest

    steps:
      - name: Checkout
        uses: actions/checkout@v2
      - name: Deploy to App Engine
        id: deploy
        uses: google-github-actions/[email protected]
        with:
          project_id: ${{ secrets.GCP_PROJECT_ID }}
          deliverables: app.yaml
          credentials: ${{ secrets.GOOGLE_APPLICATION_CREDENTIALS }}
          version: v1
      - name: Test
        run: curl "${{ steps.deploy.outputs.url }}

app.yaml:

runtime: python39

instance_class: B1
service: deploy
basic_scaling:
  max_instances: 1
  idle_timeout: 10m

Here are the two errors I'm getting:

I also get another strange error in app.yaml, which causes the workflow to not run. I thought from the Google App Engine documentation for this file that we didn't need to include an on trigger. I'm not sure if it's caused by the error in main.yaml.

Is there an easy way to fix this error?

UPDATE: After trying v0.4.0 of the GitHub Action, I get the same error, but I found out that my GOOGLE_APPLICATION_CREDENTIALS are causing the error.

{
    "type": "service_account",
    "project_id": "***",
    "private_key_id": "***",
    "private_key": "-----BEGIN PRIVATE KEY-----***=\n-----END PRIVATE KEY-----\n",
    "client_email": "***@appspot.gserviceaccount.com",
    "client_id": "***",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://oauth2.googleapis.com/token",
    "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/***%40appspot.gserviceaccount.com"
}

I replaced all private information with ***, but the JSON is definitely still valid.