(design/css) o2 dropdown (...) item isn't aligned middle & looks slightly broken when only one menu item

[hztyfoon]

For Example:
in Make WordPress Core page (​https://make.wordpress.org/core/) click the three dots icon (...) at the top right corner of any post and a dropdown the menu item 'shortlink' will appear. you'll see it doesn't look vertically centre aligned.

I also found, using 'vertical-align:middle' to the 'li' tag ('nav.o2-dropdown-actions ul li') or the 'a' tag inside the 'li' fixs it.

using 'line-height:1' to the 'li' tag also makes it center aligned.

[hztyfoon]

'Shortlink' dropdown item isn't vertically middle

[coffee2code]

In 13678:

Breathe: Ensure vertical centering for single post action link.

Props hztyfoon, coffee2code.
Fixes #6547.

(I typo'd the associated ticket getting fixed, which was supposed to be this ticket.)