fix: correctly handle injecting environment variables to deployment tasks

Also test that release tasks are invoked the correct environment.

Closes #3817

tests/apps/dockerfile-release/Dockerfile

@@ -0,0 +1,19 @@
+FROM python:3.8-buster
+
+RUN pip install --user pipenv
+ENV PATH="${PATH}:/root/.local/bin"
+ENV PIPENV_VENV_IN_PROJECT=0
+
+COPY . /app
+
+WORKDIR /app
+
+RUN ls -lah
+
+RUN rm -rf .venv
+
+RUN mkdir .venv
+
+RUN pipenv install
+
+CMD pipenv run gunicorn -b 0.0.0.0:8000 --workers=3 --threads=5 project.wsgi:application