Test failed `TestBreakIterator::testLao` with icu 70

[oxalica]

Hello,

I'm on NixOS and we recently updated a libreoffice dependency `icu` to 70.

<https://icu.unicode.org/download/70>

When building libreoffice 7.2.2.2 with `--with-system-libs`, it builds 
successfully but fails exact one unit test.

> /build/libreoffice-7.2.2.2/i18npool/qa/cppunit/test_breakiterator.cxx:865:TestBreakIterator::testLao
> equality assertion failed
> - Expected: 9
> - Actual  : 12

I can confirm that downgrading `icu` back to 69.0 fixes the test 
failure. But I'm not sure what is this test doing and I cannot read Lao. 
Does the test need updating, or there it's an issue of the new `icu` 70.0?

I also notice that the `testLao` is currently guarded and only be 
enabled if icu >51. Does it depends on some icu behaviors and we should 
also exclude it for icu >=70?

The full log of build and test can be seen here,
<https://hydra.nixos.org/log/zwqzj8n84z4kb8nscch815kypn4x6m9c-libreoffice-7.2.2.2.drv>

Thanks,
Oxalica