Try it in a working environment ... ?

.circleci/config.yml

@@ -296,19 +296,27 @@ jobs:
       - store_artifacts: *STORE_OTHER_ARTIFACTS
       - run: *SUBMIT_COVERAGE
 
-  build-porting-depgraph:
   # Generate up-to-date data for the dependency graph visualizer.
-    docker:
-      - image: "python:2.7-buster"
+  build-porting-depgraph:
+    # Get a system in which we can easily install Tahoe-LAFS and all its
+    # dependencies.  The dependency graph analyzer works by executing the code.
+    # It's Python, what do you expect?
+    <<: *DEBIAN
 
     steps:
       - "checkout"
+
       - add_ssh_keys:
           fingerprints:
             # Jean-Paul Calderone <exarkun@twistedmatrix.com> (CircleCI depgraph key)
             # This lets us push to tahoe-lafs/tahoe-depgraph in the next step.
             - "86:38:18:a7:c0:97:42:43:18:46:55:d6:21:b0:5f:d4"
 
+      - run:
+          name: "Setup Python Environment"
+          command: |
+            /tmp/venv/bin/pip install -e /tmp/project
+
       - run:
           name: "Generate dependency graph data"
           command: |