py3: add missing b prefixes in test-acl.t

There's one failure left in the test, which looks like a real problem
around executing hooks. I have not investigated further.

# skip-blame as just b'' prefixes

Differential Revision: https://phab.mercurial-scm.org/D5677

tests/test-acl.t

@@ -39,7 +39,7 b''
   >     try:
   >         return acl._getusersorig(ui, group)
   >     except:
-  >         return ["fred", "betty"]
+  >         return [b"fred", b"betty"]
   > acl._getusersorig = acl._getusers
   > acl._getusers = fakegetusers
   > EOF