Use machine executor to allow reprotests to setarch

setarch is not permittied in the docker container.
Because CircleCI only supports Ubuntu VM targets [1], we must add the Bionic sources to install dh-virtualenv under Focal as no installation candidate exists for that distribution in upstream repos.

[1] : https://circleci.com/docs/2.0/configuration-reference/#available-machine-images

.circleci/config.yml

@@ -281,15 +281,15 @@ common-steps:
 version: 2.1
 jobs:
   tests:
-    docker:
-      - image: circleci/python:3.7-buster
+    machine:
+      image: ubuntu-2004:202010-01
     steps:
       - checkout
       - run:
           name: install test requirements and run tests
           command: |
             make install-deps
-            virtualenv .venv
+            virtualenv -p python3 .venv
             source .venv/bin/activate
             pip install -r test-requirements.txt
             make test

.gitignore

@@ -1,2 +1,3 @@
+tests/__pycache__/
 debhelper-build-stamp
 *.debhelper.log

scripts/install-deps

@@ -2,6 +2,11 @@
 # Installs required dependencies for building SecureDrop Worsktation packages.
 # Assumes a Debian 10 machine, ideally a Qubes AppVM.
 
+# If running in CI, we need to add the Ubuntu Bionic repo to download dh-virtualenv
+if [[ -v CIRCLE_BUILD_URL ]]; then
+  echo "deb http://archive.ubuntu.com/ubuntu/ bionic universe" | sudo tee -a /etc/apt/sources.list
+fi
+
 sudo apt-get update
 sudo apt-get install  \
     build-essential \