Move site guides to ci

[kavya-seth-vns]

Summary

Fixes #3981

This PR moves the Site Guides workflow into the main CI workflow so that the guide tests run as part of the mandatory CI checks.

Changes

• Added the test-site-guides job to .github/workflows/ci.yml.
• Removed the standalone .github/workflows/site-guides.yml workflow.
• Ensured the site guides tests run as part of the required CI checks.

Testing

The workflow was manually triggered and verified that all site guide tests pass successfully.

Checklist

• 🛡️ Don't disclose security issues! (contact [security@apache.org](mailto:security@apache.org))
• 🔗 Clearly explained why the changes are needed, or linked related issues: Fixes Move site-guides.yml workflow into ci.yml #3981
• 🧪 Added/updated tests with good coverage, or manually tested (and explained how)
• 💡 Added comments for complex logic (not needed for this change)
• 🧾 Updated CHANGELOG.md (not required for CI workflow changes)
• 📚 Updated documentation in site/content/in-dev/unreleased (not required)

[kavya-seth-vns]

@adutra Thanks for the review! Ready to merge.

[kavya-seth-vns]

@snazy Hi! This PR has passed all CI checks and has one approval.
If everything looks good to you, it should be ready to merge. Thanks!