nixos/docs: fix typo (#372394)

            retry(tty_matches, timeout)

    def send_chars(self, chars: str, delay: float | None = 0.01) -> None:

        """

        r"""

        Simulate typing a sequence of characters on the virtual keyboard,

        e.g., `send_chars("foobar\n")` will type the string `foobar`

        followed by the Enter key.