New CSS variable for Navbars (#35829)

* Adding a brand new CSS var

* Update scss/_variables.scss

Co-authored-by: Gaël Poupard <ffoodd@users.noreply.github.com>

scss/_navbar.scss

@@ -13,6 +13,7 @@
   --#{$variable-prefix}navbar-active-color: #{$navbar-light-active-color};
   --#{$variable-prefix}navbar-brand-padding-y: #{$navbar-brand-padding-y};
   --#{$variable-prefix}navbar-brand-margin-end: #{$navbar-brand-margin-end};
+  --#{$variable-prefix}navbar-brand-font-size: #{$navbar-brand-font-size};
   --#{$variable-prefix}navbar-brand-color: #{$navbar-light-brand-color};
   --#{$variable-prefix}navbar-brand-hover-color: #{$navbar-light-brand-hover-color};
   --#{$variable-prefix}navbar-nav-link-padding-x: #{$navbar-nav-link-padding-x};
@@ -65,7 +66,7 @@
   padding-top: var(--#{$variable-prefix}navbar-brand-padding-y);
   padding-bottom: var(--#{$variable-prefix}navbar-brand-padding-y);
   margin-right: var(--#{$variable-prefix}navbar-brand-margin-end);
-  @include font-size(var(--#{$variable-prefix}navbar-toggler-font-size));
+  @include font-size(var(--#{$variable-prefix}navbar-brand-font-size));
   color: var(--#{$variable-prefix}navbar-brand-color);
   text-decoration: if($link-decoration == none, null, none);
   white-space: nowrap;