Before this commit, the portal user is assigned to the subtask if he creates a subtask via the project sharing feature. We recently hides the `Assign to me` button to those users. This commit removes the `default_user_ids` in the context used when we create a subtask in the project sharing feature to not assign the user to that new subtask. Related PR: #84006 X-original-commit: f3a241e97f80007f6d7ce2567dd22784cb35de26 Forward-port-of: #84189 Part-of: odoo/odoo#84298