fix: explicit alpine version, so dependabot detects it (#2061)

.github/dependabot.yml

@@ -21,7 +21,11 @@ updates:
     target-branch: main
   - package-ecosystem: docker
     directories:
-      - /
       - /cmd/proxy
     schedule:
       interval: weekly
+    commit-message:
+      prefix: update-docker-image
+      include: scope
+    open-pull-requests-limit: 2
+    target-branch: main

cmd/proxy/Dockerfile

@@ -6,7 +6,6 @@
 # See project Makefile if using make.
 # See docker --build-arg if building directly.
 ARG GOLANG_VERSION=1.23.5
-ARG ALPINE_VERSION=3.20
 
 FROM golang:${GOLANG_VERSION}-alpine AS builder
 
@@ -27,7 +26,7 @@ RUN DATE="$(date -u +%Y-%m-%d-%H:%M:%S-%Z)" && \
     -ldflags "-X github.com/gomods/athens/pkg/build.version=$VERSION -X github.com/gomods/athens/pkg/build.buildDate=$DATE -s -w" \
     -o /bin/athens-proxy ./cmd/proxy
 
-FROM alpine:${ALPINE_VERSION}
+FROM alpine:3.20
 ARG TARGETARCH
 
 ENV GOROOT="/usr/local/go" \