bpo-41069: Make TESTFN and the CWD for tests containing non-ascii characters. (GH-21035)

diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 3f9771b..7675a97 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -597,6 +597,7 @@
             test_cwd = 'test_python_worker_{}'.format(pid)
         else:
             test_cwd = 'test_python_{}'.format(pid)
+        test_cwd += support.FS_NONASCII
         test_cwd = os.path.join(self.tmp_dir, test_cwd)
         return test_cwd