Bug#1142824: mailman3: autopkgtest consistently fails: test_encoded_subject_not_recoded_to_list_cset

Source: mailman3
Version: 3.3.10-2
Severity: serious

mailman3's autopkgtests have been consistently failing for a while.  
Looking at https://ci.debian.net/packages/m/mailman3/testing/amd64/, 
this started between 2026-06-15 and 2026-06-19.  The failure is:

======================================================================
FAIL: test_encoded_subject_not_recoded_to_list_cset (mailman.handlers.tests.test_subject_prefix.TestSubjectPrefix.test_encoded_subject_not_recoded_to_list_cset)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/autopkgtest-lxc.y62vrv95/downtmp/build.Uig/src/src/mailman/handlers/tests/test_subject_prefix.py", line 284, in test_encoded_subject_not_recoded_to_list_cset
    self.assertEqual(decoded,
    ~~~~~~~~~~~~~~~~^^^^^^^^^
                     [(b'[Test] ', 'us-ascii'),
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^
                      (b'\xd6\xd0\xce\xc4', 'eucgb2312_cn')])
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Lists differ: [(b'[Test] ', 'us-ascii'), (b'\xd6\xd0\xce\xc4', 'gb2312')] != [(b'[Test] ', 'us-ascii'), (b'\xd6\xd0\xce\xc4', 'eucgb2312_cn')]

First differing element 1:
(b'\xd6\xd0\xce\xc4', 'gb2312')
(b'\xd6\xd0\xce\xc4', 'eucgb2312_cn')

- [(b'[Test] ', 'us-ascii'), (b'\xd6\xd0\xce\xc4', 'gb2312')]
+ [(b'[Test] ', 'us-ascii'), (b'\xd6\xd0\xce\xc4', 'eucgb2312_cn')]
?                                                   +++      +++

I think this is due to https://github.com/python/cpython/issues/88726 
having been fixed in Python 3.13.14.  It seems to have been fixed 
upstream in 
https://gitlab.com/mailman/mailman/-/commit/8e60f319009726c0014c2f2b7b3955c4fcb3d1ee.

Thanks,