pythonPackages.pytest-timeout: disable flaky test

This should fix failing NixOS tests on i686-linux.
(cherry picked from commit c4865b8933)

pkgs/development/python-modules/pytest-timeout/default.nix

@@ -21,7 +21,10 @@ buildPythonPackage rec {
   };
 
   checkInputs = [ pytest pexpect ];
-  checkPhase = ''pytest -ra'';
+  checkPhase = ''
+    # test_suppresses_timeout_when_pdb_is_entered fails under heavy load
+    pytest -ra -k 'not test_suppresses_timeout_when_pdb_is_entered'
+  '';
 
   meta = with lib;{
     description = "py.test plugin to abort hanging tests";