The example pipeline-buildah-as-user-1000 pipeline seems to not work or is incomplete. There are insufficient privileges during the fetch-repository step of the tekton pipeline.

The example was attempted using the latest version of openshift-pipelines (pipelines-1.8) on an OCP v(4.12.5) Openshift Local (formerly Red Hat CodeReady Containers) instance.

Repeatedly

Simply follow the steps in the document.
I also have a helm chart to quickly deploy the example, see https://github.com/trevorbox/buildah-unprivileged#pipeline

There are insufficient privileges for the service account.
If you view the Events in the pipeline namespace, for example:

oc get events -n test
...
51m         Warning   Failed                  pod/pipelinerun-buildah-as-user-1000-fetch-repository-pod   Error: container has runAsNonRoot and image will run as root (pod: "pipelinerun-buildah-as-user-1000-fetch-repository-pod_test(003ef27e-eeae-4024-8d46-86d939d0d6ad)", container: place-scripts)
...

The pipeline should be successful using the SCC and ServiceAccount example provided in the document.

Test chart (created from example in documentation) https://github.com/trevorbox/buildah-unprivileged#pipeline