FIX: URL encode usernames in grant admin redirect (#34664)

The grant admin action was not properly URL encoding usernames
containing unicode characters, causing broken redirect URLs when
usernames include special characters allowed by the
allowed_unicode_username_characters site setting.


https://meta.discourse.org/t/granting-admin-rights-fails-for-usernames-with-special-characters-when-admin-account-has-2fa-enabled/378063

lib/second_factor/actions/grant_admin.rb

@@ -16,7 +16,8 @@ module SecondFactor::Actions
         callback_params: {
           user_id: user.id,
         },
-        redirect_url: admin_user_show_path(id: user.id, username: user.username),
+        redirect_url:
+          CGI.unescape(admin_user_show_path(id: user.id, username: CGI.escape(user.username))),
         description: description,
       }
     end