A very very very simple approach to start a deployer deployment through GitHub Actions.

deploy.yml

name: Deployment

on:
  repository_dispatch:
    types: ['deploy']
  workflow_dispatch:
    inputs:
      deploy_host:
        description: 'Environment'
        required: true
        default: 'stag'

jobs:
  deploy-stage:
    name: Deployment
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v2

      - name: Setup PHP
        uses: shivammathur/setup-php@master
        with:
          php-version: 8.0

      - name: Install Dependencies
        run: composer install -q --no-ansi --no-interaction --no-scripts --no-progress --prefer-dist

      - name: Deploy
        uses: deployphp/action@master
        with:
          private-key: ${{ secrets.DEPLOY_KEY }}
          known-hosts: ${{ secrets.KNOWN_HOSTS }}
          dep: deploy ${{ github.event.inputs.deploy_host }} --branch=main -v