gh-124969: Skip the test for ALT_DIGITS also on iOS

[serhiy-storchaka]

• Issue: locale.nl_langinfo(locale.ALT_DIGITS) does not work #124969

[mhsmith]

!buildbot ios

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @mhsmith for commit 716c060 🤖

The command will test the builders whose names match following regular expression: ios

The builders matched are:

• iOS ARM64 Simulator PR

[freakboy3742]

As far as I can make out, skipping this test on iOS is as good as we're going to get.

The macOS and iOS langinfo.h headers both define ALT_DIGITS; but experimentally, any request to retrieve the alt digits returns an empty string. The fa_IR subtest is passing because that locale isn't defined, so it's falling back to the previously set locale (en_US). The jp_JP locale does exist, and some locale values (e.g. ABDAY_1) are defined; but ALT_DIGITS values clearly aren't.

I can't find any documentation about this beyond the man page for nl_langinfo, which doesn't shed any light on ALT_DIGITS specifically.