DOC: Fix examples gallery layout issues

Fix single column layout and extra white space caused by
pydata-sphinx-theme 0.10.0, see matplotlib#23976. This was fixed
in github.com/pydata/pydata-sphinx-theme/pull/964.

Author: StefRe

requirements/doc/doc-requirements.txt

@@ -13,7 +13,7 @@ ipython
 ipywidgets
 numpydoc>=1.0
 packaging>=20
-pydata-sphinx-theme>=0.9.0
+pydata-sphinx-theme>=0.11.0
 mpl-sphinx-theme
 sphinxcontrib-svg2pdfconverter>=1.1.0
 sphinx-gallery>=0.10