Changed get_week_number() to fix a problem with the locale en_AU

[RomainBarbason]

This is my first pull-request ever, so don't hesitate to give me feedback on anything

If my analysis is correct, get_week_number() made it impossible for iso-calendar to show their last week, because the week_number was fixed from 53 to 1, while it should be fixed to 52.
That's why the year wasn't updated and the result was "W1 2023", it should be "W52 2023".

Hope this helps !

Fixes #1133

[tomasr8]

Thanks for the PR! Do you think you could add some tests for this fix? Somewhere here might be a good place:

babel/tests/test_dates.py

Lines 715 to 720 in 313277a

	def test_datetime_format_get_week_number():
	format = dates.DateTimeFormat(date(2006, 1, 8), Locale.parse('de_DE'))
	assert format.get_week_number(6) == 1
	format = dates.DateTimeFormat(date(2006, 1, 8), Locale.parse('en_US'))
	assert format.get_week_number(6) == 2

[akx]

Yep, as Tomas said, a test would be very much appreciated - the week numbering logic seems to be pretty finicky all in all...