Upgrade to ICU 73.1

[filmil]

This is your regular once-in-6-months update of the major ICU version.

ICU 73.1 was released in mid-April 2023: https://icu.unicode.org/download/73

rust_icu sometimes has an issue with change detector tests which get tripped up by evolving CLDR information in some languages.

[filmil]

This is done.