Update alpine Docker tag to v3.23

Author: renovate[bot]

.github/actions/atlas-diff/Dockerfile

@@ -2,7 +2,7 @@
 #
 # Lighter than atlas-render — no helm/helmfile/sops needed.
 # Tools baked in: dyff, yq, jq.
-FROM alpine:3.21
+FROM alpine:3.23
 
 RUN apk add --no-cache bash curl jq
 

.github/actions/atlas-render/Dockerfile

@@ -2,7 +2,7 @@
 #
 # Tools baked in: helm, helmfile, sops, yq, jq, git.
 # Versions pinned below — Renovate manages bumps via regex.
-FROM alpine:3.21
+FROM alpine:3.23
 
 RUN apk add --no-cache bash curl git jq