ci: sync a fixed alpine version to use in future (#599)

We have been using alpine:edge which is a moving target leading to
unpredictable breakages. Let's move to numbered releases.

Signed-off-by: Ramkumar Chinchani <rchincha@cisco.com>

.github/workflows/sync-3rdparty-images.yaml

@@ -26,7 +26,7 @@ jobs:
       - name: Tag and push to ghcr
         run: |
           set -e
-          for n in ubuntu:latest alpine:edge centos:latest busybox:latest; do
+          for n in ubuntu:latest alpine:edge alpine:3.19 centos:latest busybox:latest; do
             dest="ghcr.io/${{ github.repository_owner }}/$n"
             docker trust inspect "$n"
             docker pull $n