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).