Fix detail in testing bind_dn_template

`lookup_dn` needs to be True here, because the `{username}` expansion in the `bind_dn_template` string will without it expand to fry as a login name, but needs to be expanded to `Philip J. Fry` as that is the `fry` user's cn attribute, and only such expanded dn template will successfully be found.

ldapauthenticator/tests/test_ldapauthenticator.py

@@ -66,7 +66,6 @@ async def test_ldap_auth_disallowed(c):
 )
 async def test_ldap_auth_bind_dn_template(c, bind_dn_template):
     c.LDAPAuthenticator.bind_dn_template = bind_dn_template
-    c.LDAPAuthenticator.lookup_dn = False
     authenticator = LDAPAuthenticator(config=c)
 
     # proper username and password in allowed group