Update continuous-integration.yml

https://pytest-qt.readthedocs.io/en/latest/troubleshooting.html#xvfb-assertionerror-timeouterror-when-using-waituntil-waitexposed-and-ui-events

.github/workflows/continuous-integration.yml

@@ -34,6 +34,7 @@ jobs:
         sudo apt-get install --no-install-recommends libyaml-dev libegl1-mesa libxkbcommon-x11-0 libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 libxcb-shape0 libxcb-cursor0 xserver-xephyr
         python -m pip install --upgrade pip
         pip install flake8 pytest pytest-cov pytest-qt pytest-xvfb ipython anyio
+        /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
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names
@@ -47,6 +48,7 @@ jobs:
         pip install .
         pip uninstall -y opencv-python
         pip install opencv-python-headless
+        /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
     - name: Tests
       uses: aganders3/headless-gui@v2
       with: