Doc: need to stick to sphinx-rtd-theme<1

See: readthedocs/sphinx_rtd_theme#1278

Author: MuellerSeb

setup.cfg

@@ -71,7 +71,7 @@ doc =
     pyvista>=0.29
     sphinx>=4
     sphinx-gallery>=0.8
-    sphinx-rtd-theme>=1
+    sphinx-rtd-theme<1
 plotting =
     matplotlib>=3
     pyvista>=0.29