hack(authors): bump to alpine 3.20

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

hack/dockerfiles/authors.Dockerfile

@@ -1,10 +1,11 @@
 # syntax=docker/dockerfile:1
 
-FROM alpine:3.14 AS gen
+ARG ALPINE_VERSION=3.20
+
+FROM alpine:${ALPINE_VERSION} AS gen
 RUN apk add --no-cache git
 WORKDIR /src
 RUN --mount=type=bind,target=. <<EOT
-#!/usr/bin/env bash
   set -e
   mkdir /out
   # see also ".mailmap" for how email addresses and names are deduplicated