Replace the removed cgi.parse_header() function with email.message.Message
to restore compatibility with Python 3.13 and newer.
--- ../apitools/base/protorpclite/test_util.py	2026-10-17 14:33:13.779712289 +0300
+++ ../apitools/base/protorpclite/test_util.py	2026-10-17 14:33:46.173686647 +0300
@@ -26,7 +26,6 @@
 Includes additional test utilities to make sure encoding/decoding libraries
 conform.
 """
-import cgi
 import datetime
 import inspect
 import os
@@ -34,6 +33,7 @@
 import socket
 import types
 import unittest
+from email.message import Message
 
 import six
 from six.moves import range  # pylint: disable=redefined-builtin
@@ -82,8 +82,14 @@
           header1: Header value string 1.
           header2: header value string 2.
         """
-        value1, params1 = cgi.parse_header(header1)
-        value2, params2 = cgi.parse_header(header2)
+        def parse_header(header):
+            message = Message()
+            message['content-type'] = header
+            params = message.get_params()
+            return params[0][0], dict(params[1:])
+
+        value1, params1 = parse_header(header1)
+        value2, params2 = parse_header(header2)
         self.assertEqual(value1, value2)
         self.assertEqual(params1, params2)