Remove `image` when the container block is empty

From: https://docs.github.com/en/actions/using-jobs/running-jobs-in-a-container

jobs:
  container-test-job:
    runs-on: ubuntu-latest
    container:
      image: node:14.16     

jobs:
  container-test-job:
    runs-on: ubuntu-latest
    container: node:14.16

If there is more configuration within the container block, it should stay as is. Example:

jobs:
  container-test-job:
    runs-on: ubuntu-latest
    container:
      image: node:14.16
      env:
        NODE_ENV: development
      ports:
        - 80
      volumes:
        - my_docker_volume:/volume_mount
      options: --cpus 1
    steps:
      - name: Check for dockerenv file
        run: (ls /.dockerenv && echo Found dockerenv) || (echo No dockerenv)

Start with the GitHub Actions container syntax in the linked documentation and compare the two YAML forms shown in the issue. Trace the repository's handling of container blocks, preserving the block when other configuration exists. Done means an empty container block is reduced to its image value while configured blocks remain unchanged.