Update _navbar.scss to fix navbar items in wrong position when in state "collapse in", with any navbar-toggleable-*

Created by: lvmajor

Little modification to fix the alignment problem with the nav items and the navbar-brand when viewing collapsed menu.

It's my first try at PR's so please don't be rude. If I made mistakes, I will be happy to learn from them.

Reference issue: #20392 (closed)