try once more to make docs ci work

Author: MaHaWo

.github/workflows/pypi.yml

@@ -14,7 +14,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v4
-      - uses: pyvista/setup-headless-display-action@v3
         with:
           python-version: "3.11"
       - run: pip install --upgrade build

docs/conf.py

@@ -28,6 +28,8 @@
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = [
+    "pyvista.ext.plot_directive",
+    "pyvista.ext.viewer_directive",
     "nbsphinx",
     "sphinx_rtd_theme",
     "sphinx.ext.autodoc",