Fix setting DEBIAN_FRONTEND for apt-get install

Do it in the command executed by sudo, as sudo doesn't propagate the
environment variable values by default (--preserve-env option could be
used to do it, but it's simpler to avoid it).

.github/workflows/ci_msw_cross.yml

@@ -93,8 +93,6 @@ jobs:
 
       - name: Install prerequisites
         run: |
-          export DEBIAN_FRONTEND=noninteractive
-
           packages="git make wine x11-xserver-utils xvfb"
 
           case "${HOST_TRIPLET}" in
@@ -116,7 +114,7 @@ jobs:
               ;;
           esac
 
-          sudo apt-get -qq install $packages
+          sudo DEBIAN_FRONTEND=noninteractive apt-get -qq install $packages
 
           echo "wxTEST_RUNNER=${winerun}" >> $GITHUB_ENV