Set redirect URL when building model (#12969)

Co-authored-by: Elitsa Marinovska <elm@umbraco.dk>
(cherry picked from commit 544cb30602)

src/Umbraco.Web.Website/Models/RegisterModelBuilder.cs

@@ -56,6 +56,7 @@ public class RegisterModelBuilder : MemberModelBuilderBase
 
         var model = new RegisterModel
         {
+            RedirectUrl = _redirectUrl,
             MemberTypeAlias = providedOrDefaultMemberTypeAlias,
             UsernameIsEmail = _usernameIsEmail,
             MemberProperties = _lookupProperties