ci: Add validation for Copyright headers

Strictly enforce up-to-date copyright headers using CI/CD.

.github/workflows/validate.yml

@@ -0,0 +1,35 @@
+# AUTOGENERATED COPYRIGHT HEADER START
+# Copyright (C) 2020-2023 Michael Fabian 'Xaymar' Dirks <info@xaymar.com>
+# AUTOGENERATED COPYRIGHT HEADER END
+
+name: Validate Pull Request
+
+on:
+  pull_request:
+    branches:
+      - '*'
+
+concurrency:
+  group: validate-${{ github.ref_name }}
+  cancel-in-progress: true
+
+jobs:
+  validate:
+    name: "Pull Request Validation"
+    strategy:
+      fail-fast: true
+    runs-on: "ubuntu-22.04"
+    steps:
+    - name: "Clone"
+      uses: actions/checkout@v3
+      with:
+        submodules: false
+        fetch-depth: 0
+
+    - name: "Copyright Headers"
+      shell: bash
+      run: |
+        node "tools/copyright.js" .
+        git --no-pager diff --patch --minimal HEAD --
+        git update-index --refresh
+        git diff-index --quiet HEAD --