DOC: Fixed not found links to ml-workspace in CONTRIBUTING.md

[minjk-bl]

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] New Feature
• [ ] Feature Improvement
• [ ] Refactoring
• [x] Documentation
• [ ] Other, please describe:

Description:

There's some "404 not found" links in CONTRIBUTING.md document. I changed those links from workspace to ml-workspace.

Checklist:

• [x] I have read the CONTRIBUTING document.
• [x] My changes don't require a change to the documentation, or if they do, I've added all required information.