🔨 Fix LPC1768 autodetect path on Linux (#24773)

Marlin/src/HAL/LPC1768/upload_extra_script.py

                 #
                 import getpass
                 user = getpass.getuser()
-                mpath = Path('media', user)
+                mpath = Path('/media', user)
                 drives = [ x for x in mpath.iterdir() if x.is_dir() ]
                 if target_drive in drives:  # If target drive is found, use it.
                     target_drive_found = True