[FIX] mail_activity: state of activity is TZ dependent

Have your user and your system in timezone Sao Paolo
When it is 2200 TZ time, UTC is the day after 0100

Have a activity schedule for today

Before this commit the activity was flagged as overdue.
This was because we compared the date deadline of the activity (no TZ)
to the date.today() in Python
While date do not have TZ legitimately, the moment (and place) you create them matters
Thus, we compared the date of the server (UTC -- day +1) to a date set by the user (TZ -- day -1)

After this commit we make up a date according to the user's tz
And the activity is not overdue, but in state 'today' as it should

OPW 1827920
closes #23969

addons/mail/models/mail_activity.py

@@ -2,6 +2,7 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from datetime import date, datetime, timedelta
+import pytz
 
 from odoo import api, exceptions, fields, models, _
 
@@ -108,8 +109,15 @@ class MailActivity(models.Model):
 
     @api.depends('date_deadline')
     def _compute_state(self):
-        today = date.today()
+        today_default = date.today()
+
         for record in self.filtered(lambda activity: activity.date_deadline):
+            today = today_default
+            if record.user_id.tz:
+                today_utc = pytz.UTC.localize(datetime.utcnow())
+                today_tz = today_utc.astimezone(pytz.timezone(record.user_id.tz))
+                today = date(year=today_tz.year, month=today_tz.month, day=today_tz.day)
+
             date_deadline = fields.Date.from_string(record.date_deadline)
             diff = (date_deadline - today)
             if diff.days == 0: