[FIX] website_forum: missing parenthesis for function

before this commit, on clicking on Go To Website
smart button in forum is not redirecting to the
corresponding forum due to missing parenthesis
to the function.

after this commit, on clicking the Go To Website
smart button, user is redirected to the forum.

introduced in: odoo@36c734a

closes odoo#121338

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/website_forum/models/forum.py

@@ -254,7 +254,7 @@ def get_tags_first_char(self):
 
     def go_to_website(self):
         self.ensure_one()
-        website_url = self._compute_website_url
+        website_url = self._compute_website_url()
         if not website_url:
             return False
         return self.env['website'].get_client_action(website_url)