Upgrade ICU to remove icu `-Wimplicit-int-to-float-conversion` warning.

In the version of ICU used by ZetaSQL at HEAD at the time of this writing, in `icu/source/i18n/plurrule.cpp`, there is an implicit conversion from int to float here: https://github.com/unicode-org/icu/blob/fd123bf023882f07bfacf51c39111be2f946d8f8/icu4c/source/i18n/plurrule.cpp#L1664 . This forces me to turn off the `-Wimplicit-int-to-float-conversion` warning in my project when attempting to use ZetaSQL, which is unfortunate as it is a high-value warning. I noticed that in the most recent release of ICU, this has been fixed with a `static_cast`. Would it be possible to address this issue by upgrading ZetaSQL to the most recent ICU?

Locate the ICU dependency declaration used by GoogleSQL and compare its pinned version with the release containing the fix. Review icu/source/i18n/plurrule.cpp at the referenced line to confirm the warning and then verify that the dependency upgrade removes the -Wimplicit-int-to-float-conversion warning without disabling it.

Written by the indexing model from the issue text.