ci(github-actions): add workflow dispatch for manually deployment

[Lee-W]

Description

What is the current behavior?

Cannot manually trigger deploy workflow on GitHub

What is the new behavior?

add workflow_dispatch to "Astro Deploy" workflow for enabling manually trigger deploying

Does this introduce a breaking change?

Checklist

• [ ] Created tests which fail without the change (if possible)
• [ ] Extended the README / documentation, if necessary

[Lee-W]

Glad it helps 🙂