fix Resolved Discussions counter wrapping to next line

What does this MR do?

Use flexbox for scrollable-tabs to always prevent items wrapping

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

• 2px bottom border was previously margin/padding combination. There may be some remaining 1px paddings that need removal

Screenshots (if relevant)

Only tabs tabs scrollable

separate rows:

Tabs overflow and scroll:

Discussions button right aligned:

Also fixes vertical alignment on MR tabs:

Previously:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] 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 it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #31106 (closed)