Optimize build caching

Before this commit, if docker-entrypoint or any file in mailman-web changed, the Docker build cache would not be used, so the install of dependencies would run again, uselessly

core/Dockerfile.dev

@@ -2,14 +2,10 @@
 # Use 3.15 for Core since it has Python 3.9
 FROM alpine:3.18
 
-#Add startup script to container
-COPY docker-entrypoint.sh /usr/local/bin/
-
 # Set the commits that we are building.
 ARG CORE_REF
 ARG MM3_HK_REF
 
-
 #Install all required packages, add user for executing mailman and set execution
 #rights for startup script
 RUN --mount=type=cache,target=/root/.cache \
@@ -26,6 +22,9 @@ RUN --mount=type=cache,target=/root/.cache \
     && apk del build-deps \
     && adduser -S mailman
 
+#Add startup script to container
+COPY docker-entrypoint.sh /usr/local/bin/
+
 # Change the working directory.
 WORKDIR /opt/mailman