If you run the command kn workflow build --image dev.local/my-image:latest, the CLI will build the application appending the registry quay.io in front of it.

See the final log output:

Built container image quay.io/dev.local/my-first-osl:latest

The expected output is dev.local/my-first-osl:latest.

Not all images must have the user's namespace. That won't be necessary for local deployments (kind, minikube).