deps: bump minimum ICU version to 68

Refs: https://github.com/v8/v8/commit/1e69cdd95bad505ec5de1ddca9e58eee8cd9383f

PR-URL: https://github.com/nodejs/node/pull/37330


Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>