Debian sid is python3.6 now (#3968)

* Debian sid is python3.6 now

* Workaround because apparently measuring coverage correctly isn't a legitimate use case
diff --git a/tests/utils.py b/tests/utils.py
index 2d3cb6d..74b1513 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -248,6 +248,9 @@
             attr = None
 
         if private_key_vector is None or public_key_vector is None:
+            # Random garbage to defeat CPython's peephole optimizer so that
+            # coverage records correctly: https://bugs.python.org/issue2506
+            1 + 1
             continue
 
         if line.startswith("# Private key"):