Fix Rumba32 variant for Marlin (#21497)

ini/stm32f4.ini

@@ -277,17 +277,26 @@ build_flags       = ${stm_flash_drive.build_flags}
 # RUMBA32
 #
 [env:rumba32]
-platform        = ${common_stm32.platform}
-extends         = common_stm32
-build_flags     = ${common_stm32.build_flags}
+platform             = ${common_stm32.platform}
+extends              = common_stm32
+build_flags          = ${common_stm32.build_flags}
   -Os
   -DHAL_PCD_MODULE_ENABLED
   -DDISABLE_GENERIC_SERIALUSB
   -DHAL_UART_MODULE_ENABLED
   -DTIMER_SERIAL=TIM9
-board           = rumba32_f446ve
-upload_protocol = dfu
-monitor_speed   = 500000
+board                = rumba32_f446ve
+upload_protocol      = dfu
+monitor_speed        = 500000
+board_build.core     = stm32
+board_build.variant  = MARLIN_F446VE
+board_build.ldscript = ldscript.ld
+board_build.offset   = 0x0000
+board_build.encrypt  = No
+board_build.firmware = firmware.bin
+extra_scripts        = ${common.extra_scripts}
+  pre:buildroot/share/PlatformIO/scripts/generic_create_variant.py
+  buildroot/share/PlatformIO/scripts/stm32_bootloader.py
 
 #
 # MKS Robin Pro V2