The scheduler-run script classified CNB-based images as `herokuish` because
`is_image_herokuish_based` returns true for them, which caused the
`docker-args-process-run` trigger for builder-pack to skip injecting
`--entrypoint launcher`. Without that flag the container fell back to the
image entrypoint (`/cnb/process/web`) and dropped the user-supplied
arguments. Mirror the deploy-side detection so CNB images set
`IMAGE_SOURCE_TYPE=pack`, allowing the launcher entrypoint to be added.
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