🩹 Don't use colon after error code in message text for flake8

[s-weigand]

The error code in the message passed to flake8 should not end with : since this causes problems with tools like yesqa that parse the flake8 output.

E.g. this nonsense example

def f(positive_nr: int):  # noqa: DOC502
    """Does something.

    Parameters
    ----------
    positive_nr : int
        Used to do something

    Raises
    ------
    ValueError
        If ``positive_nr`` is not a positive number.
    """
    ensure_positive(positive_nr) # raise value error if positive_nr is not positive
    result = ...
    return result

In this case yesqa would remove the noqa since it sees the error code reported as DOC502: instead of DOC502 (It uses flake8 formatting string --format=%(row)d\t%(code)s) which then does not match and the noqa gets removed.

[jsh9]

Thanks @s-weigand for making this change!