[FIX] website: hide the add language separator if it is the last item

Before this commit, the add language separator was visible at the end
of the inline language switcher even if the add language link was not
displayed.

Part of #59581

task-2312878

addons/website/static/src/scss/website.scss

@@ -1240,6 +1240,9 @@ header {
     border-radius: $rounded-pill;
     vertical-align: top;
 }
+span.list-inline-item.o_add_language:last-child {
+    display: none !important; // Hide the separator if it is the last list item
+}
 
 // Footer scrolltop button
 @if o-website-value('footer-scrolltop') {