Specify logo height instead of width on log in page

What does this MR do and why?

Specifies logo height instead of width on sign up page to account for rectangular logos

What does this MR not do?

If you have a logo that's taller than wide (which should be relatively uncommon 🤔) it's not going to look great

Screenshots or screen recordings

	Before	After
Rectangular logo
Default (or square/circular) logo

How to set up and validate locally

Admin > settings > appearance > sign in/sign up pages