Fix broken rendering of adjacent code blocks

[kwankyu]

a bug seen in, for example: https://doc-release--sagemath.netlify.app/html/en/reference/structure/sage/structure/category_object#sage.structure.category_object.CategoryObject.variable_names

Compare with the fixed page: https://doc-pr-38981--sagemath.netlify.app/html/en/reference/structure/sage/structure/category_object#sage.structure.category_object.CategoryObject.variable_names

:memo: Checklist

• [x] The title is concise and informative.
• [x] The description explains in detail what this PR is about.
• [x] I have linked a relevant issue or discussion.
• [ ] I have created tests covering the changes.
• [ ] I have updated the documentation and checked the documentation preview.

:hourglass: Dependencies

[github-actions[bot]]

Documentation preview for this PR (built with commit 7279faaee85269c1601b6c7842010fc552d29a5a; changes) is ready! :tada: This preview will update shortly after each push to this PR.

[kwankyu]

Thanks!