[FIX] website_slides: avoid redirect to /web/signup?redirect=undefined

This commit fixes the Signup link under the quiz validation.
widget.url is not defined in widget.
Now we use the redirectUrl from the widget as redirect after the signup.

It has been detected by a number of hit on /web/undefined

closes odoo/odoo#91575

X-original-commit: 8d9f22dbe109015bf62e8b563dffa30f45773d26
Signed-off-by: Romain Derie (rde) <rde@odoo.com>
Signed-off-by: Jérémy Kersten <jke@odoo.com>

addons/website_slides/static/src/xml/slide_quiz.xml

@@ -92,7 +92,7 @@
                 </div>
                 <span t-if="widget.publicUser &amp;&amp; widget.channel.signupAllowed" class="d-block mt-2">
                     <span>Don't have an account ?</span>
-                    <a class="font-weight-bold" t-att-href="'/web/signup?redirect=' + widget.url">Sign Up !</a>
+                    <a class="font-weight-bold" t-att-href="'/web/signup?redirect=' + widget.redirectURL">Sign Up !</a>
                 </span>
             </div>
             <div t-else="" class="d-md-flex align-items-center justify-content-between">