Add "Check changelog" job

.github/workflows/check-changelog.yml

@@ -0,0 +1,49 @@
+# CHANGELOG.md is generated by https://github.com/github-changelog-generator/github-changelog-generator
+# This job verifies, that it contains always the current content
+name: Check Changelog
+
+on:
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - '**.md'
+  workflow_dispatch:
+
+jobs:
+  check-changelog:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.7
+          bundler-cache: true
+
+      - name: Install github_changelog_generator
+        shell: bash
+        run: |
+          gem --user-install install github_changelog_generator
+
+      - name: Run github_changelog_generator
+        shell: bash
+        run: |
+          github_changelog_generator --token ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Compare the expected and actual CHANGELOG.md
+        run: |
+          if [ "$(git diff CHANGELOG.md | wc -l)" -gt "0" ]; then
+            echo "Detected uncommitted changes after build.  See status below:"
+            git diff
+            exit 1
+          fi
+        id: diff
+
+      # If CHANGELOG.md was different than expected, upload the expected version as an artifact
+      - uses: actions/upload-artifact@v2
+        if: ${{ failure() && steps.diff.conclusion == 'failure' }}
+        with:
+          name: changelog
+          path: CHANGELOG.md