[bug] in_prompt doesn't support "\n"

[Freed-Wu]

    def in_prompt(self) -> AnyFormattedText:
        """In prompt.

        :rtype: AnyFormattedText
        """
        FROMATS, _ = ansi2prompt_toolkit(str(sys.ps1))
        return 
            ("class:in", "In ["),
            (
                "class:in.number",
                "%s" % self.python_input.current_statement_index,
            ),
            ("class:in", "]\n>>> "),
        ]

Actual behaviour (| is cursor):

❯ ptpython
In [1] |
>>>

Expected behaviour:

❯ ptpython
In [1]
>>> |