docs: make github links reference HEAD instead of main

SIDECAR_RELEASE_PROCESS.md

@@ -95,7 +95,7 @@ naming convention `<hostpath-deployment-version>-on-<kubernetes-version>`.
 1. Check [image build status](https://k8s-testgrid.appspot.com/sig-storage-image-build).
 1. Promote images from k8s-staging-sig-storage to k8s.gcr.io/sig-storage. From
    the [k8s image
-   repo](https://github.com/kubernetes/k8s.io/tree/main/k8s.gcr.io/images/k8s-staging-sig-storage),
+   repo](https://github.com/kubernetes/k8s.io/tree/HEAD/k8s.gcr.io/images/k8s-staging-sig-storage),
    run `./generate.sh > images.yaml`, and send a PR with the updated images.
    Once merged, the image promoter will copy the images from staging to prod.
 1. Update [kubernetes-csi/docs](https://github.com/kubernetes-csi/docs) sidecar

cloudbuild.yaml

@@ -13,7 +13,7 @@
 # See https://github.com/kubernetes/test-infra/blob/HEAD/config/jobs/image-pushing/README.md
 # for more details on image pushing process in Kubernetes.
 #
-# To promote release images, see https://github.com/kubernetes/k8s.io/tree/main/k8s.gcr.io/images/k8s-staging-sig-storage.
+# To promote release images, see https://github.com/kubernetes/k8s.io/tree/HEAD/k8s.gcr.io/images/k8s-staging-sig-storage.
 
 # This must be specified in seconds. If omitted, defaults to 600s (10 mins).
 # Building three images in external-snapshotter takes roughly half an hour,