Adjust padding issue board cards

What does this MR do?

Adds a min-height to card-header so it'll be the same height independently of whether there's an assignee picture or not.

It also moves the header up 1px and the title down 2px so it'll be centered with the picture. This may fail depending on font-height.

cc @ClemMakesApps

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

Why was this MR needed?

Screenshots (if relevant)

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?