We test in proto area not in site-packages.

--- pipdeptree-2.25.0/tox.toml.orig
+++ pipdeptree-2.25.0/tox.toml
@@ -26,7 +26,7 @@
     "{tty:--color=yes}",
     { replace = "posargs", extend = true, default = [
       "--cov",
-      "{env_site_packages_dir}{/}pipdeptree",
+      "pipdeptree",
       "--cov",
       "{tox_root}{/}tests",
       "--cov-config=pyproject.toml",