chore: Install Poetry under /opt/poetry-env as non-root user

Co-authored-by: Laurent Sorber <laurent.sorber@gmail.com>

{{ cookiecutter.__package_name_kebab_case }}/Dockerfile

@@ -33,8 +33,6 @@ WORKDIR /workspaces/{{ cookiecutter.__package_name_kebab_case }}/
 
 FROM base as builder
 
-USER root
-
 # Install Poetry in separate venv so it doesn't pollute the main venv.
 ENV POETRY_VERSION 1.6.1
 ENV POETRY_VIRTUAL_ENV /opt/poetry-env
@@ -45,11 +43,11 @@ RUN --mount=type=cache,target=/root/.cache/pip/ \
 RUN ln -s $POETRY_VIRTUAL_ENV/bin/poetry /usr/bin/poetry
 
 # Install compilers that may be required for certain packages or platforms.
+USER root
 RUN --mount=type=cache,target=/var/cache/apt/ \
     --mount=type=cache,target=/var/lib/apt/ \
     apt-get update && \
     apt-get install --no-install-recommends --yes build-essential
-
 USER user
 
 # Install the run time Python dependencies in the virtual environment.