gh-149879: Fix test_httpservers on Cygwin (#150417)

Author: vstinner

Lib/test/test_httpservers.py

@@ -824,7 +824,7 @@ def test_get(self):
 
         # chmod() doesn't work as expected on Windows, and filesystem
         # permissions are ignored by root on Unix.
-        if os.name == 'posix' and os.geteuid() != 0:
+        if os.name == 'posix' and os.geteuid() != 0 and sys.platform != 'cygwin':
             os.chmod(self.tempdir, 0)
             try:
                 response = self.request(self.base_url + '/')