Reset container width when switching to pipelines MR tab

What does this MR do?

Reset container width when switching to pipelines MR tab

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1528

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

• How are karma fixture changes handled? See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10169#note_26029374

Why was this MR needed?

When using the "Side-by-side"/parallel diff view, switching from the "Changes" tab to "Pipelines" would cause "Pipelines" to also be full width.

Does this MR meet the acceptance criteria?

• 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 it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29539 (closed)