We cannot run argon2 in isolated mode because it is in proto area and so we
need to point PYTHONPATH there.

--- argon2_cffi-25.1.0/tox.ini.orig
+++ argon2_cffi-25.1.0/tox.ini
@@ -23,7 +23,7 @@
     NO_COLOR
 commands =
     pytest {posargs}
-    python -Im argon2 -n 1 -t 1 -m 8 -p 1
+    python -m argon2 -n 1 -t 1 -m 8 -p 1
     mypy: mypy tests/typing