tests: Use do_create_realm where possible.

Using do_create_realm should be preferred over manual creation where
possible, as it creates more realistic data.

zerver/tests/test_message_send.py

@@ -17,6 +17,7 @@ from zerver.lib.actions import (
     check_send_stream_message,
     do_change_can_forge_sender,
     do_change_stream_post_policy,
+    do_create_realm,
     do_create_user,
     do_deactivate_user,
     do_send_messages,
@@ -2114,7 +2115,8 @@ class InternalPrepTest(ZulipTestCase):
 
 class TestCrossRealmPMs(ZulipTestCase):
     def make_realm(self, domain: str) -> Realm:
-        realm = Realm.objects.create(string_id=domain, invite_required=False)
+        realm = do_create_realm(string_id=domain, name=domain)
+        do_set_realm_property(realm, "invite_required", False)
         RealmDomain.objects.create(realm=realm, domain=domain)
         return realm