`test_char` in `test_structmembers` fails on s390x

[colesbury]

After merging #123211:

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-rhel8-s390x.lto-pgo/build/Lib/test/test_capi/test_structmembers.py", line 170, in test_char
    self.assertEqual(ts.T_CHAR, "c")
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
AssertionError: '\x00' != 'c'
- �
+ c

https://buildbot.python.org/#/builders/509/builds/7885

cc @dpdani @vstinner

Linked PRs

• gh-127572: Temporarily skip failing test on s390x #127573
• gh-127572: Fix test_structmembers initialization #127577