Update:
buildbot@x064:[/home/buildbot/buildarea/3.x.aixtools-aix-power6/issue]./python -m test -v test_bdb
== CPython 3.8.0a0 (heads/master-dirty:0785889468, Jan 30 2019, 16:16:31) [C]
== AIX-1-00C291F54C00-powerpc-32bit big-endian
== cwd: /home/buildbot/buildarea/3.x.aixtools-aix-power6/issue/build/test_python_11862246
== CPU count: 8
== encodings: locale=ISO8859-15, FS=iso8859-15
Run tests sequentially
0:00:00 [1/1] test_bdb
test_down (test.test_bdb.StateTestCase) ... ok
...
test_step_at_return_with_no_trace_in_caller (test.test_bdb.IssuesTestCase) ... ok

======================================================================
FAIL: test_skip (test.test_bdb.StateTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.aixtools-aix-power6/issue/Lib/test/test_bdb.py", line 731, in test_skip
    tracer.runcall(tfunc_import)
  File "/home/buildbot/buildarea/3.x.aixtools-aix-power6/issue/Lib/test/test_bdb.py", line 448, in __exit__
    self.test_case.fail(err_msg)
  File "/home/buildbot/buildarea/3.x.aixtools-aix-power6/issue/Lib/test/test_bdb.py", line 582, in fail
    raise self.failureException(msg) from None
AssertionError: encoding with 'iso8859-15' codec failed (BdbNotExpectedError: Wrong event type at expect_set item 2, got 'call'
  Expected: ('line', 3, 'tfunc_import')
  Got:      ('call', 11, 'encode'),         ('quit',),)

----------------------------------------------------------------------

Ran 31 tests in 0.392s

Is this somehow related to "encoding" as in AIX is not using utf-8 as default?