Abbreviated months are incorrect for en-AU

[Daniel Becroft]

For the `en-AU` culture, the abbreviated months are incorrect. They should be 3-character months, but `June`, `July` are the ful name, and `September` is appreviated to `Sept` (should be `Sep`).

This looks to be a recent change, as v67.1 works, but 69.1 onwards is incorrect.

From the `release-67-1` branch, the `en-AU.txt` file contains:

monthNames{
    format{
        narrow{
            "J",
            "F",
            "M",
            "A",
            "M",
            "J",
            "J",
            "A",
            "S",
            "O",
            "N",
            "D",
        }
    }
    stand-alone{
        abbreviated{
            "Jan",
            "Feb",
            "Mar",
            "Apr",
            "May",
            "Jun",
            "Jul",
            "Aug",
            "Sep",
            "Oct",
            "Nov",
            "Dec",
        }
        wide{
            "January",
            "February",
            "March",
            "April",
            "May",
            "June",
            "July",
            "August",
            "September",
            "October",
            "November",
            "December",
        }
    }
}
It looks like this was changed under https://unicode-org.atlassian.net/browse/ICU-21249#icft=ICU-21249 "integrate CLDR release 38 alpha0" to include the monthNames.format.abbreviated section:

monthNames{
    format{
        abbreviated{
            "Jan",
            "Feb",
            "Mar",
            "Apr",
            "May",
            "June",
            "July",
            "Aug",
            "Sept",
            "Oct",
            "Nov",
            "Dec",
        }
        narrow{
            "J",
            "F",
            "M",
            "A",
            "M",
            "J",
            "J",
            "A",
            "S",
            "O",
            "N",
            "D",
        }
    }
    stand-alone{
        abbreviated{
            "Jan",
            "Feb",
            "Mar",
            "Apr",
            "May",
            "Jun",
            "Jul",
            "Aug",
            "Sep",
            "Oct",
            "Nov",
            "Dec",
        }
        wide{
            "January",
            "February",
            "March",
            "April",
            "May",
            "June",
            "July",
            "August",
            "September",
            "October",
            "November",
            "December",
        }
    }
} 

The format.abbreviated section, and the stand-alone.abbreviated sections, IMO (and as an Australian) should be the same. 

I’ve raise a bug in the Jira instance (https://unicode-org.atlassian.net/browse/CLDR-16718), not sure if that was the correct thing to do. I'm having trouble tracking down the changelog or discussions around this change. I can't see it mentioned (or anything related) mentioned in the CLDR 38 release notes/changelog, but I could be missing something obvious.

Thanks,

Daniel.