[FIX] website_forum: edit post with tags

Tags are lost when editing a post as we handle the wrong parameter.
Editing a post should not erase its tags anymore.

addons/website_forum/controllers/main.py

@@ -358,7 +358,7 @@ class WebsiteForum(http.Controller):
     def post_save(self, forum, post, **kwargs):
         if 'post_name' in kwargs and not kwargs.get('post_name').strip():
             return request.website.render('website.http_error', {'status_code': _('Bad Request'), 'status_message': _('Title should not be empty.')})
-        post_tags = forum._tag_to_write_vals(kwargs.get('post_tag', ''))
+        post_tags = forum._tag_to_write_vals(kwargs.get('post_tags', ''))
         vals = {
             'tag_ids': post_tags,
             'name': kwargs.get('post_name'),