Update docker to use pipx rather than a curl command

Dockerfile

@@ -6,7 +6,9 @@ COPY . /app/
 FROM base as install-poetry
 ENV POETRY_VIRTUALENVS_CREATE=false \
     POETRY_VERSION=1.5.1
-RUN curl -sSL https://install.python-poetry.org | python3 -
+
+RUN pip install pipx
+RUN pipx install poetry==$POETRY_VERSION
 RUN apt-get update && apt-get install -y --no-install-recommends gcc
 ENV PATH "/root/.local/bin:$PATH"