Update .gitea/workflows/deploy-pages.yml

added graphiz for the collaboration diagrams

.gitea/workflows/deploy-pages.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Install system dependencies
         run: |
           apt-get update
-          apt-get install -y doxygen
+          apt-get install -y doxygen graphviz
 
       - name: Build musrfit-tech-docu
         run: |