One MARLIN_DEV_MODE warning per rebuild (#19163)

Marlin/src/MarlinCore.cpp

 
 #include "MarlinCore.h"
 
+#if ENABLED(MARLIN_DEV_MODE)
+  #warning "WARNING! Disable MARLIN_DEV_MODE for the final build!"
+#endif
+
 #include "HAL/shared/Delay.h"
 #include "HAL/shared/esp_wifi.h"
 

Marlin/src/inc/SanityCheck.h

 #endif
 #undef HEXIFY
 
-#if ENABLED(MARLIN_DEV_MODE)
-  #warning "WARNING! Disable MARLIN_DEV_MODE for the final build!"
-#endif
-
 /**
  * Warnings for old configurations
  */