Upgrade to Alpine 3.19

Tested amd64 and arm64 builds locally, and tested the arm64 image on my
local Hypcast server without issue.

Dockerfile

@@ -1,8 +1,8 @@
 # syntax = docker.io/docker/dockerfile:1.6
 
 # The Alpine and Go base images must use the same release of Alpine.
-ARG ALPINE_BASE=docker.io/library/alpine:3.18
-ARG GOLANG_BASE=docker.io/library/golang:1.21-alpine3.18
+ARG ALPINE_BASE=docker.io/library/alpine:3.19
+ARG GOLANG_BASE=docker.io/library/golang:1.21-alpine3.19
 # The Node.js image does not require any particular OS.
 ARG NODEJS_BASE=docker.io/library/node:20-alpine
 # See https://gstreamer.freedesktop.org/download/.