Save some time and skip installing packages that are already there (microsoft#153467)

Author: alexdima

.github/workflows/ci.yml

@@ -106,8 +106,6 @@ jobs:
       # TODO: rename azure-pipelines/linux/xvfb.init to github-actions
       - name: Setup Build Environment
         run: |
-          sudo apt-get update
-          sudo apt-get install -y libxkbfile-dev pkg-config libsecret-1-dev libxss1 dbus xvfb libgtk-3-0 libgbm1
           sudo cp build/azure-pipelines/linux/xvfb.init /etc/init.d/xvfb
           sudo chmod +x /etc/init.d/xvfb
           sudo update-rc.d xvfb defaults