Merge pull request #1041 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: unidata-pr-helper[bot]

ci-dev/doc_requirements.txt

@@ -3,5 +3,5 @@ matplotlib==3.10.7
 metpy==1.7.1
 sphinx==8.2.3
 sphinx_rtd_theme==3.0.1
-sphinx-gallery==0.20.0
+sphinx-gallery==0.21.0
 myst-parser==5.0.0