Replaced unused `new-gl-button` with `gl-button`

What does this MR do?

Looks like there's some refs to a non-existent new-gl-button class. Let's update these to gl-button 🎉

Screenshots (strongly suggested)

The following have been updated and now have a button style consistent with the rest of the app 🎉

Render mermaid diagram warning	Application Settings > Integrations	Auto Devops Enabled	No SSH Warning

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content