Fix/double registration of core video block (#45967)

* run Jetpack video block regisration late so we can detect if it's been registered already

* changelog

* Fix dumb error, thanks linting

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/19453629776

Upstream-Ref: Automattic/jetpack@3fde352

Author: grzegorz-cp