eliot-tree: use `addBinToPathHook`

pkgs/by-name/el/eliot-tree/package.nix

···
   lib,
   python3Packages,
   fetchPypi,
+  addBinToPathHook,
 }:
 
 python3Packages.buildPythonApplication rec {
···
   ];
 
   nativeCheckInputs = with python3Packages; [
+    addBinToPathHook
     pytestCheckHook
     testtools
   ];
-
-  # Tests run eliot-tree in out/bin.
-  preCheck = ''
-    export PATH=$out/bin:$PATH
-  '';
 
   pythonImportsCheck = [ "eliottree" ];