CI: Github Action: run "apt-get update" before packages restore

ubuntu somehow needs it, no idea why does not apt-get do it itself.

.github/workflows/vtest.yml

@@ -46,6 +46,7 @@ jobs:
     - name: Install apt dependencies
       if: ${{ startsWith(matrix.os, 'ubuntu-') }}
       run: |
+        sudo apt-get update
         sudo apt-get install -y \
           liblua5.3-dev \
           libpcre2-dev \