try xvfb for CI testing with GUI

Author: chrissimpkins

.github/workflows/python-ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest]
         python-version: [3.9]
 
     steps:
@@ -21,6 +21,8 @@ jobs:
           python -c "import sys; print(sys.version)"
           python -c "import struct; print(struct.calcsize('P') * 8)"
       - name: Install testing dependencies
-        run: python -m pip install --upgrade pip setuptools wheel tox tox-gh-actions
+        run: |
+          sudo apt install libxkbcommon-x11-0 libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 libxcb-xfixes0
+          python -m pip install --upgrade pip setuptools wheel tox tox-gh-actions pytest pytest-qt pytest-xvfb
       - name: Run tox tests
         run: python -m tox