Fix pipelines table headers

What does this MR do?

Removed stages loop for a single 'Stages' header.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The headers were messing the table up. Note the redundant headers and squished cells.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #22472 (closed)