Add doxygen to dependencies

Author: trgwii

.github/workflows/CI.yml

@@ -11,7 +11,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get -y install check
+          sudo apt-get -y install check doxygen
 
       - name: Checkout
         uses: actions/checkout@v4