Fix to test the new milestone offset

Dockerfile

@@ -5,6 +5,8 @@ FROM --platform=linux/amd64 heroku/heroku:${STACK_VERSION}-build as build
 ARG STACK_VERSION
 ENV STACK="heroku-${STACK_VERSION}"
 
+ARG GOOGLE_CHROME_MILESTONE_OFFSET
+
 # On Heroku-24 and later the default user is not root.
 # Once support for Heroku-22 and older is removed, the `useradd` steps below can be removed.
 USER root
@@ -15,6 +17,9 @@ USER non-root-user
 RUN mkdir -p /tmp/build /tmp/cache /tmp/env
 COPY --chown=non-root-user . /buildpack
 
+# Emulate the platform providing app config vars via env directory
+RUN if [ -n "${GOOGLE_CHROME_MILESTONE_OFFSET}" ]; then echo "${GOOGLE_CHROME_MILESTONE_OFFSET}" > /tmp/env/GOOGLE_CHROME_MILESTONE_OFFSET; fi
+
 # Sanitize the environment seen by the buildpack, to prevent reliance on
 # environment variables that won't be present when it's run by Heroku CI.
 RUN env -i PATH=$PATH HOME=$HOME STACK=$STACK /buildpack/bin/detect /tmp/build

bin/test.sh

@@ -27,7 +27,7 @@ docker run --rm heroku-buildpack-chrome-for-testing bash -l -c 'du --human-reada
 
 
 # Verify that the milestone offset builds too
-docker build --progress=plain --build-arg="STACK_VERSION=${STACK_VERSION}" --build-arg="GOOGLE_CHROME_MILESTONE_OFFSET=-4" -t heroku-buildpack-chrome-for-testing .
+docker build --progress=plain --build-arg="STACK_VERSION=${STACK_VERSION}" --build-arg="GOOGLE_CHROME_MILESTONE_OFFSET=-4" -t heroku-buildpack-chrome-for-testing --no-cache .
 
 # Check the profile.d scripts correctly added the binaries to PATH.
 docker run --rm heroku-buildpack-chrome-for-testing bash -l -c 'chrome --version'