Fix warning for ESP32 (#16771)

Marlin/src/HAL/HAL_ESP32/timers.cpp

 
   timer_enable_intr(timer.group, timer.idx);
 
-  timer_isr_register(timer.group, timer.idx, timer_isr, (void*)timer_num, 0, nullptr);
+  timer_isr_register(timer.group, timer.idx, timer_isr, (void*)(uint32_t)timer_num, 0, nullptr);
 
   timer_start(timer.group, timer.idx);
 }