In case anyone is curious, this is the commit that implements the change: https://github.com/GrapheneOS/platform_packages_apps_CellBro...

EDIT: For folks with rooted devices, all alerts can be disabled with:

    adb shell su -c 'pm disable com.google.android.cellbroadcastreceiver'

and reenabled with:

    adb shell su -c 'pm enable com.google.android.cellbroadcastreceiver'

For folks on custom Android builds (or older stock Android builds without APEX module support), the package name is `com.android.cellbroadcastreceiver` (without the `.google`).