ulwgl_util: fix bug for copyfile arguments

- Changes the second argument for copyfile, as the second should not be joined.

- When failing to make a shallow copy on a non-CoW filesystem, we fallback to normal copying by utilizing the shutil module. However, the second argument was wrong, as the state of the parameters are simply the files themselves that should be copied to the destination. For instance:

/usr/share/ULWGL/run-in-sniper             (source)
/home/foo/.local/share/ULWGL/run-in-sniper (destination)

ulwgl_util.py

@@ -291,7 +291,7 @@ def copyfile_reflink(src: Path, dst: Path) -> None:
                 raise
             if e.errno == ENOSYS:
                 # Fallback to normal copy
-                copyfile(src.as_posix(), dst.joinpath(src.name).as_posix())
+                copyfile(src.as_posix(), dst.as_posix())
 
         dst.chmod(src.stat().st_mode)