CI add LLVM repos

.gitea/workflows/docs.yaml

@@ -7,11 +7,17 @@ on:
 
 jobs:
   build-and-deploy:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Check out repository
         uses: actions/checkout@v4
 
+      - name: Add LLVM APT repo
+        run: |
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 21
+
       - name: Install software
         run: |
           sudo apt-get update