Added missing closing brace in sample code for safe HTML translations

Closes #19321. [ci skip]

guides/source/i18n.md

@@ -707,7 +707,7 @@ you can safely pass the username as set by the user:
 
 ```erb
 <%# This is safe, it is going to be escaped if needed. %>
-<%= t('welcome_html', username: @current_user.username %>
+<%= t('welcome_html', username: @current_user.username) %>
 ```
 
 Safe strings on the other hand are interpolated verbatim.