FIXUP: Do not use --no-root flag

The `make test` command relies on importing the dangerzone library,
which is why we must do `poetry install` without the `--no-root` flag.

See: python-poetry/poetry#1868

dev_scripts/env.py

@@ -94,12 +94,18 @@
 RUN echo user:2000:2000 > /etc/subuid
 RUN echo user:2000:2000 > /etc/subgid
 
+# XXX: We need the empty source folder, so that we can trick Poetry to create a
+# link to the project's path. This way, we should be able to do `import
+# dangerzone` from within the container.
+RUN mkdir -p /home/user/dangerzone/dangerzone
+RUN touch /home/user/dangerzone/dangerzone/__init__.py
+
 USER user
 WORKDIR /home/user
 VOLUME /home/user/dangerzone
 
 COPY pyproject.toml poetry.lock /home/user/dangerzone/
-RUN cd /home/user/dangerzone && poetry install --no-root
+RUN cd /home/user/dangerzone && poetry install
 """
 
 DOCKERFILE_BUILD_DEBIAN_DEPS = r"""