bpo-38347: use os.sep instead of the Unix specific '/'

Fix a test failure on Windows by using os.sep instead of the Unix
specific '/' as path separator.

Author: rpluem

Lib/test/test_tools/test_pathfix.py

@@ -17,7 +17,7 @@ def setUp(self):
         self.temp_directory = support.TESTFN + '.d'
         self.addCleanup(support.rmtree, self.temp_directory)
         os.mkdir(self.temp_directory)
-        self.temp_file = self.temp_directory + '/' + \
+        self.temp_file = self.temp_directory + os.sep + \
                          os.path.basename(support.TESTFN) + '-t.py'
         self.addCleanup(support.unlink, self.temp_file)