CI: Run apt install before installing libxml2-utils, GHA cache got flaky

Author: akien-mga

.github/workflows/static_checks.yml

@@ -15,6 +15,7 @@ jobs:
 
       - name: Install APT dependencies
         run: |
+          sudo apt update
           sudo apt install -y libxml2-utils
 
       - name: Install Python dependencies and general setup