test(helpers): upgrade ct-helpers to 1.3.9

rebar.config.erl

@@ -99,7 +99,7 @@ test_plugins() ->
 
 test_deps() ->
     [ {bbmustache, "1.10.0"}
-    , {emqx_ct_helpers, {git, "https://github.com/emqx/emqx-ct-helpers", {tag, "1.3.6"}}}
+    , {emqx_ct_helpers, {git, "https://github.com/emqx/emqx-ct-helpers", {tag, "1.3.9"}}}
     , meck
     ].