Remove left margin for stages with downstream and only one job

What does this MR do?

Removes left margin being set to 0 for stages with just one job that links to a downstream:

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #2714