feat: set concurrency_limit on tektoncd/pipeline Repository CR

Set concurrency_limit: 2 on the tektoncd-pipeline PAC Repository to
prevent all release branches from building simultaneously. Without this,
the weekly patch-release cron triggers 7-8 concurrent multi-arch ko
builds that exhaust tekton-nodepool node memory, causing kubelet hangs
(see #3428).

With concurrency_limit: 2, PAC queues excess PipelineRuns and starts
them as running ones complete.

Related: #3428

Author: vdemeester

tekton/cd/pipelines-as-code/overlays/oci-ci-cd/repositories/pipeline.yaml

@@ -28,6 +28,7 @@ metadata:
   name: tektoncd-pipeline
   namespace: releases-pipeline
 spec:
+  concurrency_limit: 2
   url: "https://github.com/tektoncd/pipeline"
   settings:
     # Fetch .tekton/ from the default branch (main), not from the PR branch.