A simple GitHub workflow that is able to detect the changes of the configured files/directories and execute other steps (e.g. adding comments) based on the output

file-watcher-workflow.yml

name: Changelog check

on:
  pull_request:
    branches: [ main ]
env:
  MESSAGE_ID: "${{ github.ref_name }}-changelog-comment"
jobs:
  check-changelog:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v3
    - name: Get changed files
      id: changed-files
      uses: tj-actions/changed-files@v34
      with:
        files: |
          CHANGES.md
    - name: Upsert comment if CHANGES.md has not been changed
      if: steps.changed-files.outputs.any_modified != 'true'
      uses: mshick/add-pr-comment@v2
      with:
        message: |
          **⚠️ CHANGES.md has not been changed**
          That might be totally fine, but please make it sure that you didn't forget to update it!
        message-id: ${{ env.MESSAGE_ID }}
    - name: Upsert comment if CHANGES.md has been changed
      if: steps.changed-files.outputs.any_modified == 'true'
      uses: mshick/add-pr-comment@v2
      with:
        message: |
          **✅ CHANGES.md has been changed**
          It doesn't mean that it contains a useful entry, but at least it was modified.
        message-id: ${{ env.MESSAGE_ID }}