upgrade Dockerfile deps and use HEREDOC syntax

Signed-off-by: Pierre Fenoll <pierrefenoll@gmail.com>

Dockerfile

@@ -1,7 +1,7 @@
-# syntax=docker.io/docker/dockerfile:1@sha256:42399d4635eddd7a9b8a24be879d2f9a930d0ed040a61324cfdf59ef1357b3b2
+# syntax=docker.io/docker/dockerfile:1.3-labs@sha256:250ce669e1aeeb5ffb892b18039c3f0801466536cb4210c8eb2638e628859bfd
 
-FROM --platform=$BUILDPLATFORM docker.io/library/alpine:3.16 AS alpine
-FROM --platform=$BUILDPLATFORM gcr.io/distroless/base:nonroot@sha256:02f667185ccf78dbaaf79376b6904aea6d832638e1314387c2c2932f217ac5cb AS distroless
+FROM --platform=$BUILDPLATFORM docker.io/library/alpine:3.17 AS alpine
+FROM --platform=$BUILDPLATFORM gcr.io/distroless/base:nonroot@sha256:e406b1da09bc455495417a809efe48a03c48011a89f6eb57b0ab882508021c0d AS distroless
 
 FROM alpine AS osmap-linux
 RUN echo linux   >/os
@@ -14,17 +14,18 @@ FROM osmap-$TARGETOS AS osmap
 FROM alpine AS fetcher
 WORKDIR /app
 RUN \
-    --mount=from=osmap,source=/os,target=/os \
-    set -ux \
- && apk add --no-cache curl \
- && export url=https://github.com/bojand/ghz/releases \
- && export arch=x86_64 \
- && export VERSION=$( ( curl -#fSLo /dev/null -w '%{url_effective}' $url/latest && echo ) | while read -r x; do basename $x; done) \
- && curl -#fSLo exe.tar.gz $url/download/$VERSION/ghz-$(cat /os)-$arch.tar.gz \
- && curl -#fSLo sha2 $url/download/$VERSION/ghz-$(cat /os)-$arch.tar.gz.sha256 \
- && sha256sum exe.tar.gz | grep -F $(cat sha2) \
- && tar xvf exe.tar.gz \
- && rm ghz-web* && mkdir exe && mv ghz* exe/
+    --mount=from=osmap,source=/os,target=/os <<EOF
+set -eux
+apk add --no-cache curl
+export url=https://github.com/bojand/ghz/releases
+export arch=x86_64
+export VERSION=$( ( curl -#fSLo /dev/null -w '%{url_effective}' $url/latestecho ) | while read -r x; do basename $x; done)
+curl -#fSLo exe.tar.gz $url/download/$VERSION/ghz-$(cat /os)-$arch.tar.gz
+curl -#fSLo sha2 $url/download/$VERSION/ghz-$(cat /os)-$arch.tar.gz.sha256
+sha256sum exe.tar.gz | grep -F $(cat sha2)
+tar xvf exe.tar.gz
+rm ghz-web* && mkdir exe && mv ghz* exe/
+EOF
 
 FROM scratch AS ghz-binary
 COPY --from=fetcher /app/exe/* /