Actions: Add change note checker

Co-authored-by: Taus <tausbn@github.com>

.github/workflows/check-change-note.yml

@@ -0,0 +1,33 @@
+on:
+  pull_request_target:
+    types: [labeled, unlabeled, opened, synchronize, reopened, ready_for_review]
+    paths:
+      - "*/ql/src/**/*.ql"
+      - "*/ql/src/**/*.qll"
+      - "!**/experimental/**"
+
+jobs:
+  check-change-note:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check if change note file is present
+        uses: dorny/paths-filter@7c0f15b688b020e95e00f15c61299b022f08ca95 # v2.8.0
+        id: paths_filter
+        with:
+          filters: |
+            change_note:
+              - '**/change-notes/*.md'
+      - name: Get PR labels
+        id: pr-labels
+        uses: joerick/pr-labels-action@0a4cc4ee0ab557ec0b1ae1157fa6fa7f9f4c494b # v1.0.6
+      - name: Fail if change note is missing
+        uses: actions/github-script@v3
+        if: |
+          github.event.pull_request.draft == false &&
+          steps.paths_filter.outputs.change_note == 'false' &&
+          !contains(steps.pr-labels.outputs.labels, ' no-change-note-required ')
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            core.setFailed('No change note found.' +
+            ' Either add one, or add the `no-change-note-required` label.')