[FIX] website: sign-up in multi-website

- Create 2 companies A & B
- For each company, create a website linked to a different URL and
  activate 'Free sign up' and 'Specific User Account'.
- As a public user, go to website of company B
- Go to 'Sign in > Don't have an account?' and create an account

The user is created in company A (the company of the user template)
instead of company B (the company of the website).

We set the company of the user based on the company of the website.

opw-1962197

closes odoo/odoo#32823

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/website/models/res_users.py

@@ -35,10 +35,12 @@ class ResUsers(models.Model):
 
     @api.model
     def _signup_create_user(self, values):
-        new_user = super(ResUsers, self)._signup_create_user(values)
         current_website = self.env['website'].get_current_website()
         if request and current_website.specific_user_account:
-            new_user.website_id = current_website
+            values['company_id'] = current_website.company_id.id
+            values['company_ids'] = [(4, current_website.company_id.id)]
+            values['website_id'] = current_website.id
+        new_user = super(ResUsers, self)._signup_create_user(values)
         return new_user
 
     @api.model