github: Fix Ubuntu package installation.

Before trying to install a package, APT cache must be updated to avoid
asking for an unavailable version of a package.

Fixes: 6cb2f5a630 ("github: Add GitHub Actions workflow.")
Signed-off-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

.github/workflows/build-and-test.yml

@@ -133,6 +133,8 @@ jobs:
         path: dpdk-dir
         key:  ${{ env.matrix_key }}-${{ env.ci_key }}
 
+    - name: update APT cache
+      run:  sudo apt update
     - name: install common dependencies
       if:   matrix.deb_package == ''
       run:  sudo apt install -y ${{ env.dependencies }}