Don't empty ALPINE_VERSION

This reverts commit 6c0ae9349d.

Dockerfile

@@ -13,6 +13,7 @@ ARG GID=991
 ### Build Hardened Malloc
 FROM docker.io/alpine:${ALPINE_VERSION} as build-malloc
 
+ARG HARDENED_MALLOC_VERSION
 ARG CONFIG_NATIVE=false
 
 COPY thestinger.gpg /tmp/
@@ -24,8 +25,13 @@ RUN apk --no-cache add build-base git gnupg && cd /tmp \
 
 
 ### Build Mastodon
+ARG ALPINE_VERSION
+
 FROM docker.io/alpine:${ALPINE_VERSION} as mastodon-build
 
+ARG MASTODON_VERSION
+ARG MASTODON_REPOSITORY
+
 # Install build dependencies
 RUN apk --no-cache add -t build-dependencies \
     build-base \
@@ -67,8 +73,13 @@ RUN yarn install --pure-lockfile --ignore-engines \
 
 
 ### Mastodon runtime
+ARG ALPINE_VERSION
+
 FROM docker.io/alpine:${ALPINE_VERSION} as mastodon
 
+ARG UID
+ARG GID
+
 ENV RUN_DB_MIGRATIONS=true \
     SIDEKIQ_WORKERS=5 \
     BIND=0.0.0.0 \