Scripts/Pet: Fix npc_pet_gen_soul_trader not following owner (#23772)

(cherry picked from commit 8ecc45cd1aac1c33c8b4cb2f269ac24d728570cc)

src/server/scripts/Pet/pet_generic.cpp

@@ -344,6 +344,8 @@ struct npc_pet_gen_soul_trader : public ScriptedAI
         Talk(SAY_SOUL_TRADER_INTRO);
         if (Unit* owner = me->GetOwner())
             DoCast(owner, SPELL_ETHEREAL_ONSUMMON);
+
+        CreatureAI::JustAppeared();
     }
 };