deps: update ICU to 70 RC
Refs: https://github.com/unicode-org/icu/releases/tag/release-70-rc
Do not land! This is only to test/run CI
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Refs: https://github.com/unicode-org/icu/releases/tag/release-70-rc
Do not land! This is only to test/run CI