#15872: Be flexible with appending *.* in shutil.rmtree test case

The Windows buildbots seem to be unable to agree whether they need them or not.
diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
index 1eb5e89..9509d2a 100644
--- a/Lib/test/test_shutil.py
+++ b/Lib/test/test_shutil.py
@@ -132,7 +132,7 @@
         filename = os.path.join(tmpdir, "tstfile")
         with self.assertRaises(OSError) as cm:
             shutil.rmtree(filename)
-        if os.name == 'nt':
+        if cm.exception.filename.endswith('*.*'):
             rm_name = os.path.join(filename, '*.*')
         else:
             rm_name = filename