Merge pull request #4046 from Unidata/dependabot-pip-ci-dev-sphinx-gallery-0.21.0

CI: (deps): Bump sphinx-gallery from 0.20.0 to 0.21.0 in /ci-dev

Author: dopplershift

ci-dev/doc_requirements.txt

@@ -1,6 +1,6 @@
 sphinx==9.0.4
 pydata-sphinx-theme==0.16.1
 sphinx-design==0.7.0
-sphinx-gallery==0.20.0
+sphinx-gallery==0.21.0
 myst-parser==5.0.0
 geopandas==1.1.2