Change voxel sandcastle categories

[jjspace]

Description

In #11909 we missed switching the cesium-sandcastle-labels away from Development so they still show up under that category even though they are in the main Gallery folder.

Issue number and link

No issue

Testing plan

• npm run build-release to generate gallery-list without the development examples
• npm start -- --production to prevent it rebuilding the gallery list when starting
• Load Sandcastle and check for
  • http://localhost:8080/Apps/Sandcastle/index.html?src=Voxels.html loads still
  • http://localhost:8080/Apps/Sandcastle/index.html?src=Voxel%20Picking.html loads still
  • Both sandcastles show up under the "Showcases" category AND the "3D Tiles" category

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have update the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @jjspace!

✅ We can confirm we have a CLA on file for you.

[ggetz]

Thanks @jjspace!