pyopenssl needs pretend for its tests now (#3739)

diff --git a/Jenkinsfile b/Jenkinsfile
index 50f53a2..fab5de7 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -105,7 +105,7 @@
             source .venv/bin/activate
             pip install ../cryptography
             pip install -e .
-            pip install pytest
+            pip install pytest pretend
             pytest tests
         """
     ],