Core/Vehicles: Treat entering other vehicles mounted on main vehicle as swapping seats

(cherry picked from commit 110564e757fefbfbddfab876a96ca9eb5aa7dd7b)

src/server/game/Spells/Auras/SpellAuraEffects.cpp

@@ -3083,7 +3083,10 @@ void AuraEffect::HandleAuraControlVehicle(AuraApplication const* aurApp, uint8 m
                 caster->ToCreature()->RemoveCorpse();
         }
 
-        if (!(mode & AURA_EFFECT_HANDLE_CHANGE_AMOUNT))
+        bool seatChange = (mode & AURA_EFFECT_HANDLE_CHANGE_AMOUNT)                             // Seat change on the same direct vehicle
+            || target->HasAuraType(SPELL_AURA_CONTROL_VEHICLE);                                 // Seat change to a proxy vehicle (for example turret mounted on a siege engine)
+
+        if (!seatChange)
             caster->_ExitVehicle();
         else
             target->GetVehicleKit()->RemovePassenger(caster);  // Only remove passenger from vehicle without launching exit movement or despawning the vehicle