Limit baud rate to 460800 on Darwin (MacOS)

Author: PaulZC

RTK_Firmware_Uploader/RTK_Firmware_Uploader.py

@@ -375,7 +375,8 @@ def update_baud_rates(self) -> None:
         # Highest speed first so code defaults to that
         # if settings.value(SETTING_BAUD_RATE) is None
         self.baud_combobox.clear()
-        self.baud_combobox.addItem("921600", 921600)
+        if (platform.system() != "Darwin"): # 921600 fails on MacOS
+            self.baud_combobox.addItem("921600", 921600)
         self.baud_combobox.addItem("460800", 460800)
         self.baud_combobox.addItem("115200", 115200)