Pin it in the tox configuration

Because why should setup.py matter?

.circleci/config.yml

@@ -89,19 +89,19 @@ workflows:
       - "typechecks":
           <<: *DOCKERHUB_CONTEXT
 
-  # images:
-  #   # Build the Docker images used by the ci jobs.  This makes the ci jobs
-  #   # faster and takes various spurious failures out of the critical path.
-  #   triggers:
-  #     # Build once a day
-  #     - schedule:
-  #         cron: "0 0 * * *"
-  #         filters:
-  #           branches:
-  #             only:
-  #               - "master"
+  images:
+    # Build the Docker images used by the ci jobs.  This makes the ci jobs
+    # faster and takes various spurious failures out of the critical path.
+    triggers:
+      # Build once a day
+      - schedule:
+          cron: "0 0 * * *"
+          filters:
+            branches:
+              only:
+                - "master"
 
-  #   jobs:
+    jobs:
       - "build-image-debian-10":
           <<: *DOCKERHUB_CONTEXT
       - "build-image-debian-9":

setup.py

@@ -96,10 +96,7 @@ install_requires = [
     #   an sftp extra in Tahoe-LAFS, there is no point in having one.
     # * Twisted 19.10 introduces Site.getContentFile which we use to get
     #   temporary upload files placed into a per-node temporary directory.
-    #
-    # * Twisted 21.2.0 introduces some type hints which we are not yet
-    #   compatible with.
-    "Twisted[tls,conch] >= 19.10.0, <21.2.0",
+    "Twisted[tls,conch] >= 19.10.0",
 
     "PyYAML >= 3.11",
 

tox.ini

@@ -120,6 +120,9 @@ deps =
     mypy
     git+https://github.com/Shoobx/mypy-zope
     git+https://github.com/warner/foolscap
+    # Twisted 21.2.0 introduces some type hints which we are not yet
+    # compatible with.
+    # https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3622
     twisted<21.2.0
 commands = mypy src