Fix job services localhost example in workflow-syntax-for-github-actions.md

[piotrekkr]

Why:

Because job services localhost example is wrong and misleading.

What's being changed (if available, include any code snippets, screenshots, or gifs):

Current example states that :

When you specify the Docker host port but not the container port, the container port is randomly assigned to a free port. GitHub sets the assigned container port in the ${{job.services.<service_name>.ports}} context. In this example, you can access the service container ports using the ${{ job.services.nginx.ports['8080'] }} and ${{ job.services.redis.ports['6379'] }} contexts.

Which is not true because you either specify container port only and then GitHub Actions will choose random free port on host, or you specify both, host and container port.

To access host port you should use container port as a key. In nginx example it should be ${{ job.services.nginx.ports['80'] }} and not 8080.

Updated job services yaml example to show more clearly how to access those services.

I tested all this using this yaml

jobs:
  job-a:
    runs-on: ubuntu-latest
    services:
      nginx:
        image: nginx
        # Map port 8080 on the Docker host to port 80 on the nginx container
        ports:
          - 8080:80
      redis:
        image: redis
        # Map TCP port 6379 on Docker host to a random free port on the Redis container
        ports:
          - 6379/tcp
    steps:
      - run: docker ps
      - run: echo '${{ toJSON(job.services) }}'
      - run: |
          echo "Redis available on 127.0.0.1:${{ job.services.redis.ports['6379'] }}"
          echo "Nginx available on 127.0.0.1:${{ job.services.nginx.ports['80'] }}"
      - name: Check Redis
        run: |
          echo -e '*1\r\n$4\r\nPING\r\n' | netcat -w1 127.0.0.1 ${{ job.services.redis.ports['6379'] }}

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[github-actions]

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Source	Preview	Production	What Changed
actions/using-workflows/workflow-syntax-for-github-actions.md	fpt ghec ghes@ 3.13 3.12 3.11 3.10 3.9	fpt ghec ghes@ 3.13 3.12 3.11 3.10 3.9

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ghec: GitHub Enterprise Cloud
ghes: GitHub Enterprise Server

[nguyenalex836]

@piotrekkr Thanks so much for opening a PR! I'll get this triaged for review ✨