Add the gh-pages branch to the build gate workflow (#205)

# Pull Request

## 📖 Description

<!--- Provide some background and a description of your work. -->
The build gate must pass for `gh-pages` branch, this update adds that branch to the workflow file.

## ✅ Checklist

### General

<!--- Review the list and put an x in the boxes that apply. -->

- [ ] I have added tests for my changes.
- [ ] I have tested my changes.
- [x] I have updated the project documentation to reflect my changes.

## ⏭ Next Steps

<!---
If there is relevant follow-up work to this PR, please list any existing issues or provide brief descriptions of what you would like to do next.
-->
- Merge this change into the `gh-pages` branch

.github/workflows/ci-validate.yml

@@ -4,10 +4,12 @@ on:
   push:
     branches: 
       - main
+      - gh-pages
       - 'features/**'
   pull_request:
     branches: 
       - main
+      - gh-pages
       - 'features/**'
 
 jobs: