Re-add flex-grow to .navbar-collapse (#32899)

Update .navbar-collapse to drop width 100 and use flex-grow, restoring it to v4's behavior

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

scss/_navbar.scss

@@ -109,10 +109,10 @@
 // the default flexbox row orientation. Requires the use of `flex-wrap: wrap`
 // on the `.navbar` parent.
 .navbar-collapse {
+  flex-grow: 1;
   // For always expanded or extra full navbars, ensure content aligns itself
   // properly vertically. Can be easily overridden with flex utilities.
   align-items: center;
-  width: 100%;
 }
 
 // Button for toggling the navbar when in its collapsed state