[EuiTour] Add extra spacing between the `title` and `subtitle`

[cchaos]

EuiTour could now use a little extra spacing between the title and subtitle, I'll create a follow up for this as well.

Originally posted by @cchaos in #5842 (comment)

---

Once #5842 merges, and EuiTour is taken up for conversion, we'll want to add a tiny bit of space to make up for the change in line-height.

Before

After

[github-actions]

👋 Hey there. This issue hasn't had any activity for 180 days. We'll automatically close it if that trend continues for another week. If you feel this issue is still valid and needs attention please let us know with a comment.

[github-actions]

❌ We're automatically closing this issue due to lack of activity. Please comment if you feel this was done in error.

[cee-chen]

@miukimiu or @daveyholler do you mind grabbing this?