ci: Update bot should enable the tests #22115
Description
When update bot post an update PR like #22112 they post a ok-to-build-image and ok-to-build-iso comments to trigger image and iso builds. When the image and iso are ready, a reviewer need to add /ok-to-test comment to start the test.
It would be useful if this is managed automatically, and the /ok-to-test comment will be added when the both image and iso are ready.
Another more declerative option: post /ok-to-test comment together with the ok-to-build-* comments, but make the system smarter, waiting for image and iso before starting the tests.