Why is citext/regress failing on hamerkop?

For example, 'i'::citext = 'İ'::citext fails to be true.

It must now be using UTF-8 (unlike, say, Drongo) and non-C ctype,
given that the test isn't skipped. This isn't the first time that
we've noticed that Windows doesn't seem to know about İ→i (see [1]),
but I don't think anyone has explained exactly why, yet. It could be
that it just doesn't know about that in any locale, or that it is
locale-dependent and would only do that for Turkish, the same reason
we skip the test for ICU, or ...

Either way, it seems like we'll need to skip that test on Windows if
we want hamerkop to be green. That can probably be cribbed from
collate.windows.win1252.sql into contrib/citext/sql/citext_utf8.sql's
prelude... I just don't know how to explain it in the comment 'cause I
don't know why.

One new development in Windows-land is that the system now does
actually support UTF-8 in the runtime libraries[2]. You can set it at
a system level, or for an application at build time, or by adding
".UTF-8" to a locale name when opening the locale (apparently much
more like Unix systems, but I don't know what exactly it does). I
wonder why we see this change now... did hamerkop have that ACP=UTF-8
setting applied on purpose, or if computers in Japan started doing
that by default instead of using Shift-JIS, or if it only started
picking UTF-8 around the time of the Meson change somehow, or the
initdb-template change. It's a little hard to tell from the logs.

[1] https://www.postgresql.org/message-id/CAC%2BAXB10p%2BmnJ6wrAEm6jb51%2B8%3DBfYzD%3Dw6ftHRbMjMuSFN3kQ%40mail.gmail.com
[2] https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page