ci: add license header validation check (#27)

Fixes #18

Confirmed it works by removing the license header for `CMakeLists.txt`
here:
https://github.com/google/ml-flashpoint/pull/27/checks?sha=7bb36ee0cf3c9d14ff2a74e532f6e39afacf0350

Author: g-husam

.github/workflows/build_and_test.yml

@@ -80,8 +80,8 @@ jobs:
           --gcov-ignore-parse-errors negative_hits.warn \
           --gcov-ignore-parse-errors suspicious_hits.warn
 
-  lint:
-    runs-on: ubuntu-24.04-32core
+  lint-code:
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version: [ "3.10" ]
@@ -108,3 +108,20 @@ jobs:
         sudo apt-get update && sudo apt-get install -y clang-format
         clang-format --version
         find src -name '*.cpp' -o -name '*.h' | xargs clang-format --dry-run --Werror
+
+  lint-license:
+    runs-on: ubuntu-latest
+    steps:
+    - name: 'Checkout Code'
+      uses: 'actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8' # ratchet:actions/checkout@v5
+
+    - name: 'Set up Go'
+      uses: 'actions/setup-go@d35c59abb061a4a6fb18e82ac0862c26744d6ab5' # ratchet:actions/setup-go@v5
+      with:
+        go-version: '1.24'
+        cache: true
+
+    - name: 'Validate License Headers'
+      shell: 'bash'
+      run: |
+        go run github.com/google/addlicense@v1.1.1 -check -s=only .