Issue #20220: Add DST rules to work around glibc quirk

This was triggering intermittent failures in unrelated tests.
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index 96b4f32..838411e 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -55,7 +55,9 @@
                 '"18-May-2033 05:33:20 +0200"']
 
     @run_with_locale('LC_ALL', 'de_DE', 'fr_FR')
-    @run_with_tz('STD-1DST')
+    # DST rules included to work around quirk where the Gnu C library may not
+    # otherwise restore the previous time zone
+    @run_with_tz('STD-1DST,M3.2.0,M11.1.0')
     def test_Time2Internaldate(self):
         expected = '"18-May-2033 05:33:20 +0200"'