buildPythonPackage: rename nix_run_setup.py to nix_run_setup

If the extension is .py it tends to be picked up by tools, breaking for
example tests.

pkgs/development/python-modules/natsort/default.nix

@@ -39,9 +39,7 @@ buildPythonPackage rec {
     sha256 = "9ffbfb74bf3fc3905be1b9b052ed865675651e38fcd972ed1ed5c64a02f93cbd";
   };
 
-  # do not run checks on nix_run_setup.py
-  patches = lib.singleton ./setup.patch
-         ++ lib.optional (isPy35 || isPy36) ./python-3.6.3-test-failures.patch;
+  patches = lib.optional (isPy35 || isPy36) ./python-3.6.3-test-failures.patch;
 
   # testing based on project's tox.ini
   checkPhase = ''

pkgs/development/python-modules/natsort/setup.patch

@@ -1,20 +0,0 @@
-diff --git a/setup.cfg b/setup.cfg
-index 604994d..e38c3ec 100644
---- a/setup.cfg
-+++ b/setup.cfg
-@@ -6,6 +6,7 @@ formats = gztar
- 
- [tool:pytest]
- flakes-ignore = 
-+	nix_run_setup.py ALL
- 	natsort/compat/py23.py UndefinedName
- 	natsort/__init__.py UnusedImport
- 	natsort/compat/* UnusedImport
-@@ -14,6 +15,7 @@ flakes-ignore =
- 	test_natsort/test_locale_help.py UnusedImport RedefinedWhileUnused
- 	test_natsort/compat/* UnusedImport
- pep8ignore = 
-+	nix_run_setup.py ALL
- 	natsort/ns_enum.py E126 E241 E123 E221
- 	test_natsort/test_*.py E501 E241 E221
- 	test_natsort/test_natsort_keygen.py E501 E241 E221 E701