Ubuntu test fixes

Author: mrvisscher

.github/workflows/testing.yaml

@@ -16,7 +16,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-13, macos-latest]
         py-version: ["3.10", "3.11", "3.12"]
     env:
-      DISPLAY: ':99.0'
+      QT_QPA_PLATFORM: 'offscreen'
     steps:
       - uses: actions/checkout@v4
 
@@ -28,10 +28,7 @@ jobs:
 
       - name: Install linux dependencies
         if: ${{ matrix.os == 'ubuntu-latest' }}
-        # https://pytest-qt.readthedocs.io/en/latest/troubleshooting.html#github-actions
-        run: |
-          sudo apt install libxkbcommon-x11-0 libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 libxcb-xfixes0 x11-utils
-                  /sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -screen 0 1920x1200x24 -ac +extension GLX
+        uses: tlambert03/setup-qt-libs@v1
 
       - name: Update pip & install testing pkgs
         run: |