[FIX] calendar: Mark activity as done with text

Issue:
======
Marking an activity of calender event as marked with text raises an
error.

Steps to reproduce the issue:
=============================
-Go to any contact and create a meeting with him as an activity in the
chatter.
- Mark the actvity as done and add some text as feedback.
- An error showing that the record is deleted.

The issue already solved here , this commits only add the test.

opw-3623719

closes odoo/odoo#146045

X-original-commit: 787f2f44961b9b5283b7bdc944acc2e8284212cc
Signed-off-by: Mahdi Cheikh Rouhou (macr) <macr@odoo.com>

addons/calendar/tests/test_mail_activity_mixin.py

@@ -75,3 +75,5 @@ class TestMailActivityMixin(MailCommon):
             act1.calendar_event_id = ev1
 
             self.assertEqual(test_record.activity_calendar_event_id.name, ev1.name, "This should be the calendar event of the next activity")
+
+            act1._action_done(feedback="Mark activity as done with text")