test: Add copyright-check workflow

.github/workflows/check-copyright.yml

@@ -0,0 +1,21 @@
+name: Copyright years
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  changed_files:
+    runs-on: ubuntu-latest
+    name: Test changed-files
+    steps:
+      - name: Get changed files
+        id: changed-files
+        uses: tj-actions/changed-files@v44
+      - name: where
+        run: pwd
+      - name: Check changed files
+        env:
+          ALL_CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
+        run: perl ./ietf/check-copyright -l -f ${ALL_CHANGED_FILES};