fix(data_import): rm duplicate import call and fix test

apps/emqx_management/src/emqx_mgmt_data_backup.erl

@@ -525,7 +525,6 @@ do_import_conf(RawConf, Opts) ->
     Errors =
         lists:foldr(
             fun(Module, ErrorsAcc) ->
-                Module:import_config(RawConf),
                 case Module:import_config(RawConf) of
                     {ok, #{changed := Changed}} ->
                         maybe_print_changed(Changed, Opts),

apps/emqx_management/test/emqx_mgmt_data_backup_SUITE.erl

@@ -440,8 +440,8 @@ create_test_tab(Attributes) ->
 
 apps_to_start() ->
     [
-        {emqx_conf, "dashboard.listeners.http.bind = 0"},
         {emqx, #{override_env => [{boot_modules, [broker, router]}]}},
+        {emqx_conf, #{config => #{dashboard => #{listeners => #{http => #{bind => <<"0">>}}}}}},
         emqx_psk,
         emqx_management,
         emqx_dashboard,