MDEV-30889: 1 - Allocation in Item_subselect::mark_as_dependent

Fix leack in Item_subselect::mark_as_dependent (allocation
of temporary list in statement memory inctroduced in
f4d55210 )

sql/item_subselect.cc

@@ -400,11 +400,11 @@ bool Item_subselect::mark_as_dependent(THD *thd, st_select_lex *select,
   {
     is_correlated= TRUE;
     Ref_to_outside *upper;
-    if (!(upper= new (thd->stmt_arena->mem_root) Ref_to_outside()))
+    if (!(upper= new (thd->mem_root) Ref_to_outside()))
       return TRUE;
     upper->select= select;
     upper->item= item;
-    if (upper_refs.push_back(upper, thd->stmt_arena->mem_root))
+    if (upper_refs.push_back(upper, thd->mem_root))
       return TRUE;
   }
   return FALSE;