Revert to non-action version

.github/workflows/test_branches.yml

@@ -53,6 +53,9 @@ jobs:
     name: ${{ matrix.TARGET }}/${{ matrix.python }}${{ matrix.other }}
     runs-on: ${{ matrix.os }}
     timeout-minutes: 120
+    env:
+      DISPLAY: ':99.0'
+      QT_SELECT: 'qt6'
     strategy:
       fail-fast: false
       matrix:
@@ -195,7 +198,11 @@ jobs:
         #  - contrib.viewer needs: libg1l libegl1
         sudo apt-get -o Dir::Cache=${GITHUB_WORKSPACE}/cache/os \
             install libopenblas-dev gfortran liblapack-dev glpk-utils
+        sudo apt-get -o Dir::Cache=${GITHUB_WORKSPACE}/cache/os \
+            install -y xvfb x11-utils libxkbcommon-x11-0 libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 libxcb-xinerama0 libxcb-xfixes0 xdotool
         sudo chmod -R 777 ${GITHUB_WORKSPACE}/cache/os
+        # start xvfb in the background
+        sudo /usr/bin/Xvfb $DISPLAY -screen 0 1280x1024x24 &
 
     - name: Update Windows
       if: matrix.TARGET == 'win'
@@ -215,15 +222,6 @@ jobs:
         auto-update-conda: false
         python-version: ${{ matrix.python }}
 
-    # This is necessary for qt (UI) tests; the package utilized here does not
-    # have support for OSX.
-    - name: Set up UI testing infrastructure
-      if: ${{ matrix.TARGET != 'osx' }}
-      uses: pyvista/setup-headless-display-action@v2
-      with:
-        qt: true
-        pyvista: true
-
     # GitHub actions is very fragile when it comes to setting up various
     # Python interpreters, expecially the setup-miniconda interface.
     # Per the setup-miniconda documentation, it is important to always