[3.1.x] Fixed #31790 -- Fixed setting SameSite and Secure cookies flags in HttpResponse.delete_cookie().

Cookies with the "SameSite" flag set to None and without the "secure"
flag will be soon rejected by latest browser versions.

This affects sessions and messages cookies.
Backport of 240cbb63bf from master

tests/messages_tests/test_cookie.py

@@ -1,5 +1,6 @@
 import json
 
+from django.conf import settings
 from django.contrib.messages import constants
 from django.contrib.messages.storage.base import Message
 from django.contrib.messages.storage.cookie import (
@@ -85,6 +86,10 @@ class CookieTests(BaseTests, SimpleTestCase):
         self.assertEqual(response.cookies['messages'].value, '')
         self.assertEqual(response.cookies['messages']['domain'], '.example.com')
         self.assertEqual(response.cookies['messages']['expires'], 'Thu, 01 Jan 1970 00:00:00 GMT')
+        self.assertEqual(
+            response.cookies['messages']['samesite'],
+            settings.SESSION_COOKIE_SAMESITE,
+        )
 
     def test_get_bad_cookie(self):
         request = self.get_request()