Update alpine Docker tag to v3.21.3

Author: renovate[bot]

alpine/Dockerfile

@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1.13.0
-ARG VERSION=3.21.2
+ARG VERSION=3.21.3
 
 # =========================================================
 FROM alpine:$VERSION AS overlay

builder/Dockerfile

@@ -7,7 +7,7 @@ RUN \
 CGO_ENABLED=0 go build -o /go/bin/init -v --ldflags '-s -w -extldflags=-static'
 
 # =========================================================
-FROM alpine:3.21.2 AS image
+FROM alpine:3.21.3 AS image
 SHELL ["/bin/ash", "-euxo", "pipefail", "-c"]
 RUN apk add --no-cache \
 bash \

emulator/Dockerfile

@@ -7,7 +7,7 @@ RUN --mount=from=claylinux/alpine-virt:latest,target=/system build-image --forma
 
 # =========================================================
 # Generate a qemu image running our custom OS image
-FROM alpine:3.21.2 AS emulator
+FROM alpine:3.21.3 AS emulator
 RUN apk add --no-cache bash qemu-system-x86_64 ovmf
 COPY entrypoint.sh /entrypoint
 ENTRYPOINT ["/entrypoint"]