CI: fix xmllint installation

by doing an apt-get update

Author: e-marchand

.github/workflows/lint.yml

@@ -23,6 +23,7 @@ jobs:
 
       - name: Lint XML
         run: |
+          sudo apt-get update
           sudo apt-get install libxml2-utils
           # shellcheck disable=2046
           find . \( -name "*.xlf" -o -name '*.4DCatalog' -o -name "*.4DSettings" \) -type f -exec xmllint --noout '{}' +