Simplify XVFB usage.

The previous system has been unreliable.  I've redone it as my own
script which I can continue to update as needed.

Author: HexDecimal

.github/workflows/python-package.yml

@@ -27,7 +27,7 @@ jobs:
     - name: Install APT dependencies
       run: |
         sudo apt update
-        sudo apt install libsdl2-dev
+        sudo apt install libsdl2-dev xvfb
     - name: Install Python dependencies
       run: |
         python -m pip install --upgrade pip
@@ -57,7 +57,6 @@ jobs:
       run: |
         python setup.py develop  # Install the package in-place.
     - name: Test with pytest
-      uses: GabrielBB/xvfb-action@v1
-      with:
-        run: pytest --cov-report=xml
+      run: |
+        xvfb-run --auto-servernum pytest --cov-report=xml
     - uses: codecov/codecov-action@v1