Do not use Literal to count in SQL

Following ce972acc1cf2, this conversion was missing and prevent psycopg 3 to
determine the data type.

trytond/trytond/res/notification.py

@@ -4,7 +4,6 @@
 import json
 from collections import defaultdict
 
-from sql import Literal
 from sql.aggregate import Count
 
 from trytond.bus import Bus
@@ -149,7 +148,7 @@ class Notification(
         notification = cls.__table__()
         cursor = Transaction().connection.cursor()
         cursor.execute(*notification.select(
-                Count(Literal('*')),
+                Count(),
                 where=((notification.user == Transaction().user)
                     & notification.unread)))
         return cursor.fetchone()[0]

trytond/trytond/tests/test_chat.py

@@ -49,6 +49,7 @@ class NotificationTestCase(TestCase):
         self.assertEqual(message.audience, 'public')
         self.assertEqual(message.content, "Chat Message: Bar")
         with Transaction().set_user(alice.id):
+            self.assertEqual(Notification.get_count(), 1)
             notification, = Notification.get()
             self.assertEqual(notification, {
                     'id': notification['id'],