chore(tests): fix import and export test cases for auth mnesia

apps/emqx_management/test/emqx_auth_mnesia_migration_SUITE.erl

@@ -67,8 +67,8 @@ init_per_testcase(_, Config) ->
     Config.
 
 end_per_testcase(_, _Config) ->
-    ok = mnesia:clear_table(emqx_acl),
-    ok = mnesia:clear_table(emqx_user),
+    {atomic,ok} = mnesia:clear_table(emqx_acl),
+    {atomic,ok} = mnesia:clear_table(emqx_user),
     ok.
 
 t_matrix(Config) ->