test: fix compile warnings in test suites

apps/emqx/integration_test/emqx_persistent_session_ds_SUITE.erl

@@ -516,7 +516,7 @@ do_t_session_expiration(_Config, Opts) ->
 
 t_session_gc(Config) ->
     GCInterval = ?config(gc_interval, Config),
-    [Node1, Node2, Node3] = Nodes = ?config(nodes, Config),
+    [Node1, Node2, _Node3] = Nodes = ?config(nodes, Config),
     CoreNodes = [Node1, Node2],
     [
         Port1,

apps/emqx_dashboard/test/emqx_swagger_requestBody_SUITE.erl

@@ -315,6 +315,8 @@ t_none_ref(_Config) ->
     ),
     ok.
 
+namespace() -> undefined.
+
 t_sub_fields(_Config) ->
     Spec = #{
         post => #{