chore(CI): attempt to fix the Mailman CI gate

[vytas7]

Trying various options to address this CI failure: https://github.com/falconry/falcon/actions/runs/3557778912/jobs/6035948328:

FAIL: test_uheader_multiline (mailman.handlers.tests.test_cook_headers.TestCookHeaders)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/github/workspace/.ecosystem/mailman/src/mailman/handlers/tests/test_cook_headers.py", line 65, in test_uheader_multiline
    self.assertEqual(header.encode(), 'A multiline [...]')
AssertionError: '=?utf-8?b?QSBtdWx0aWxpbmUgWy4uLl0=?=' != 'A multiline [...]'
- =?utf-8?b?QSBtdWx0aWxpbmUgWy4uLl0=?=
+ A multiline [...]

[codecov[bot]]

Codecov Report

Merging #2134 (a081f54) into master (5b9e1ff) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #2134   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           55        55           
  Lines         5553      5553           
  Branches       880       880           
=========================================
  Hits          5553      5553           

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[vytas7]

Doesn't seem to help :grimacing: @maxking do you have any ideas maybe? These tests succeed locally in Docker for me, as well as in GitLab...