[FIX] fixup: add_members -> _add_members

Author: nd-dew

addons/mail/tests/test_call_artifact.py

@@ -47,7 +47,7 @@ def test_admin_access(self):
     def test_user_access_member(self):
         # Membership grants read access to the channel's calls,
         # which in turn grants read access to the call's artifacts
-        self.channel.add_members(partner_ids=[self.user_employee.partner_id.id])
+        self.channel._add_members(partners=self.user_employee.partner_id)
         artifact = self.artifact.with_user(self.user_employee)
 
         self.assertTrue(artifact.read(["start_ms"]), "Channel member should be able to read artifact")