🔨 Update SKR 3 env (#24711)

ini/stm32h7.ini

 #
 [env:STM32H743Vx_btt]
 extends                     = stm32_variant
-platform                    = ststm32@~14.1.0
-platform_packages           = framework-arduinoststm32@https://github.com/stm32duino/Arduino_Core_STM32/archive/main.zip
+platform                    = ststm32@~15.4.1
+platform_packages           = framework-arduinoststm32@~4.20200.220530
 board                       = marlin_STM32H743Vx
 board_build.offset          = 0x20000
 board_upload.offset_address = 0x08020000