ci: update packages before installation

This prevents the error:

E: Failed to fetch mirror+file:/etc/apt/apt-mirrors.txt/pool/main/libx/libxml2/libxml2-utils_2.9.14%2bdfsg-1.3ubuntu3.4_amd64.deb  404  Not Found

Author: brotkrueml

.github/workflows/xliff.yml

@@ -23,6 +23,7 @@ jobs:
           fetch-depth: 1
       - name: Install package
         run: |
+          sudo apt-get update
           sudo apt-get -y install libxml2-utils
       - name: Validate XLIFF files
         run: |