build(deps): bump sphinx-design from 0.5.0 to 0.6.0 in /lib/spack/docs (#44360)

Bumps [sphinx-design](https://github.com/executablebooks/sphinx-design) from 0.5.0 to 0.6.0.
- [Release notes](https://github.com/executablebooks/sphinx-design/releases)
- [Changelog](https://github.com/executablebooks/sphinx-design/blob/main/CHANGELOG.md)
- [Commits](https://github.com/executablebooks/sphinx-design/compare/v0.5.0...v0.6.0)

---
updated-dependencies:
- dependency-name: sphinx-design
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

lib/spack/docs/requirements.txt

@@ -1,6 +1,6 @@
 sphinx==7.2.6
 sphinxcontrib-programoutput==0.17
-sphinx_design==0.5.0
+sphinx_design==0.6.0
 sphinx-rtd-theme==2.0.0
 python-levenshtein==0.25.1
 docutils==0.20.1