[IMP] project: avoid to add OdooBot as default assignee on tasks

During the creation of a private task (model project.task with not
project_id set), the current user is added as assignee. For all the demo
data, OdooBot is therefore added as a default assignee. This commit
avoid this situation by performing a check on user id at creation of a
private task.

task-3085077

addons/project/models/project_task.py

@@ -897,7 +897,7 @@ class Task(models.Model):
                 vals['date_assign'] = fields.Datetime.now()
                 if not project_id:
                     user_ids = self._fields['user_ids'].convert_to_cache(vals.get('user_ids', []), self)
-                    if self.env.user.id not in user_ids:
+                    if self.env.user.id not in list(user_ids) + [SUPERUSER_ID]:
                         vals['user_ids'] = [Command.set(list(user_ids) + [self.env.user.id])]
             # Stage change: Update date_end if folded stage and date_last_stage_update
             if vals.get('stage_id'):