buildPythonPackage: always add interpreter to passthru

pkgs/top-level/python-packages.nix

@@ -78,6 +78,7 @@ let
       # Use passthru in order to prevent rebuilds when possible.
       passthru = (oldAttrs.passthru or {})// {
         pythonModule = python;
+        inherit python;
         pythonPath = [ ]; # Deprecated, for compatibility.
         requiredPythonModules = requiredPythonModules drv.propagatedBuildInputs;
       };
@@ -92,6 +93,7 @@ let
         # used by `nix-env`.
         name = removePythonPrefix oldAttrs.name;
         pythonModule = false;
+        inherit python;
       };
     });