Update Stylelint rules

Enable `scss/selector-no-union-class-name`

scss/_navbar.scss

@@ -155,6 +155,7 @@
     $next: breakpoint-next($breakpoint, $grid-breakpoints);
     $infix: breakpoint-infix($next, $grid-breakpoints);
 
+    // stylelint-disable-next-line scss/selector-no-union-class-name
     &#{$infix} {
       @include media-breakpoint-up($next) {
         flex-wrap: nowrap;