chore: keep OCI format

Default changed to docker, but we want to keep OCI as we have no need to
support docker format in our deployments.

Signed-off-by: Martin Basti <mbasti@redhat.com>

Author: Martin Basti

.tekton/image-controller-pull-request.yaml

@@ -114,7 +114,7 @@ spec:
       name: build-platforms
       type: array
     - name: buildah-format
-      default: docker
+      default: oci
       type: string
       description: The format for the resulting image's mediaType. Valid values are oci or docker.
     results:

.tekton/image-controller-push.yaml

@@ -111,7 +111,7 @@ spec:
       name: build-platforms
       type: array
     - name: buildah-format
-      default: docker
+      default: oci
       type: string
       description: The format for the resulting image's mediaType. Valid values are oci or docker.
     results: