gh-43521: Skip the HTTPGzipHandler tests when zlib is unavailable

HTTPGzipHandler() raises ImportError without zlib, so on builds that
lack it (such as the MSan CI job) twelve of the tests errored instead
of being skipped.

Author: soreavis

Lib/test/test_urllib2.py

@@ -1968,6 +1968,7 @@ def close(self):
         self._file.close()
 
 
+@support.requires_zlib()
 class HTTPGzipHandlerTests(unittest.TestCase):
 
     body = b"The quick brown fox jumps over the lazy dog.\n" * 200