Update Alpine to the latest image cached in GitHub Actions, 3.16 (#91)

See https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2204-Readme.md#cached-docker-images

ecs/Dockerfile

@@ -37,7 +37,7 @@ RUN mkdir runtime \
     && cp -r /ejabberd/sql lib/ejabberd-*/priv
 
 # Runtime container
-FROM alpine:3.14
+FROM alpine:3.16
 ARG VERSION
 ARG VCS_REF
 ARG BUILD_DATE

mix/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.14
+FROM alpine:3.16
 LABEL maintainer="ProcessOne <contact@process-one.net>" \
       product="Ejabberd mix development environment"