Add 8.5.6 CHANGELOG items

[ci skip]

CHANGELOG

@@ -39,6 +39,9 @@ v 8.6.0 (unreleased)
   - Move group activity to separate page
   - Continue parameters are checked to ensure redirection goes to the same instance
+v 8.5.6
+  - Obtain a lease before querying LDAP
+
 v 8.5.5
   - Ensure removing a project removes associated Todo entries
   - Prevent a 500 error in Todos when author was removed