Pin Docker image alpine:3.16.2

alpine:3.16.2
->
alpine:3.16.2@sha256:bc41182d7ef5ffc53a40b044e725193bc10142a1243f395ee852a8d9730fc2ad

 [atomist:generated]
 [atomist-skill:atomist/docker-base-image-policy]

Signed-off-by: Atomist Bot <bot@atomist.com>

docker/images/alpine-tar-zstd/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.16.2
+FROM alpine:3.16.2@sha256:bc41182d7ef5ffc53a40b044e725193bc10142a1243f395ee852a8d9730fc2ad
 
 RUN apk update \
     && apk add --no-cache pigz tar zstd \