Consolidate COPY operations into a single layer

Author: yeikel

maven/Dockerfile

@@ -2,26 +2,28 @@
 # This cannot be inlined below (e.g., COPY --from=maven:...) because Dependabot does not support that syntax yet
 FROM maven:3.9.9 as maven
 
+FROM ghcr.io/dependabot/dependabot-updater-core AS builder
+
+COPY --chown=dependabot:dependabot --from=maven /usr/share/maven $DEPENDABOT_HOME/maven-installation
+COPY --chown=dependabot:dependabot --parents maven common $DEPENDABOT_HOME/
+COPY --chown=dependabot:dependabot updater $DEPENDABOT_HOME/dependabot-updater
+
 FROM ghcr.io/dependabot/dependabot-updater-core
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     openjdk-21-jdk-headless \
     ca-certificates-java \
     && rm -rf /var/lib/apt/lists/*
 
-COPY --from=maven /usr/share/maven /usr/share/maven
+USER dependabot
 
-ENV MAVEN_HOME=/usr/share/maven
+COPY --from=builder $DEPENDABOT_HOME $DEPENDABOT_HOME
 
-RUN ln -s ${MAVEN_HOME}/bin/mvn /usr/bin/mvn
+ENV MAVEN_HOME=$DEPENDABOT_HOME/maven-installation
 
-USER dependabot
+ENV PATH="${JAVA_HOME}/bin:${MAVEN_HOME}/bin:${PATH}"
 
-ENV PATH=$JAVA_HOME/bin:$PATH
 ENV MAVEN_ARGS="-Dmaven.repo.local=$DEPENDABOT_HOME/.m2"
 
-COPY --chown=dependabot:dependabot --parents maven common $DEPENDABOT_HOME/
-COPY --chown=dependabot:dependabot updater $DEPENDABOT_HOME/dependabot-updater
-
 # symlink so script/dependabot just works
 RUN mkdir -p ~/.m2 && ln -s ~/maven/settings.xml ~/.m2/settings.xml