[FIX] hr_timesheet: add missing import

addons/hr_timesheet/models/project.py

@@ -2,6 +2,7 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from odoo import models, fields, api
+from odoo.exceptions import UserError
 
 
 class Project(models.Model):
@@ -55,4 +56,4 @@ class Task(models.Model):
                 'project_id': project_id,
                 'account_id': self.env['project.project'].browse(project_id).sudo().analytic_account_id.id
             })
-        return result
+        return result