bug#51832: Piping unicode text in `shell-command'

[Tor Kringeland]

Running

  (shell-command "echo -n '悟' | pbcopy")

or

  (shell-command "echo -n 'øøøø' | pbcopy")

fills the clipboard with `ÊÇü' and `√∏', respectively, while if I run
the same commands in a terminal emulator outside Emacs I get back the
original input.  The same happens if I run the same shell commands in
`eshell'.  This happens when I run a recent build of Emacs 29 with `-Q'
on macOS Catalina.