ci: add linter job for changelog entries

What is bad: a considerable amount of boilerplate code should be added
to just run a simple script. I hope we'll do something with this
in #6604.

(cherry picked from commit 8b1ce351)

.github/workflows/lint.yml

@@ -57,3 +57,29 @@ jobs:
           TELEGRAM_TO: ${{ secrets.TELEGRAM_CORE_TO }}
         uses: ./.github/actions/send-telegram-notify
         if: failure()
+
+  release-notes:
+    # Run on pull request only if the 'notest' label is unset and this is
+    # an external PR (internal PRs trigger a run on push).
+    if: github.event_name != 'pull_request' ||
+        ( ! contains(github.event.pull_request.labels.*.name, 'notest') &&
+          github.event.pull_request.head.repo.full_name != github.repository )
+
+    runs-on: ubuntu-20.04-self-hosted
+
+    steps:
+      # We don't need neither deep fetch, nor submodules here.
+      - uses: actions/checkout@v2.3.4
+      # Don't use actions/setup-python to don't bother with proper
+      # setup of our self-hosted machines, see [1].
+      #
+      # Any python version is okay for the script, even Python 2.
+      #
+      # [1]: https://github.com/actions/setup-python#using-setup-python-with-a-self-hosted-runner
+      - run: ./tools/gen-release-notes
+      - name: call action to send Telegram message on failure
+        env:
+          TELEGRAM_TOKEN: ${{ secrets.TELEGRAM_CORE_TOKEN }}
+          TELEGRAM_TO: ${{ secrets.TELEGRAM_CORE_TO }}
+        uses: ./.github/actions/send-telegram-notify
+        if: failure()