autopkgtest fails in focal on s390x

[Balint Reczey]

https://autopkgtest.ubuntu.com/packages/feersum/focal/s390x

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-focal/focal/s390x/f/feersum/20210105_140555_20e81@/log.gz
...
t/13-pre-fork.t ...........
1..16
ok 1 - use Feersum::Runner;
not ok 2 - client 4: http success

# Failed test 'client 4: http success'
# at t/13-pre-fork.t line 25.
# got: '599'
# expected: '200'
not ok 3 - client 4: looks good

# Failed test 'client 4: looks good'
# at t/13-pre-fork.t line 26.
# undef
# doesn't match '(?^:^Hello customer number 0x[0-9a-f]+$)'
not ok 4 - client 3: http success

# Failed test 'client 3: http success'
# at t/13-pre-fork.t line 25.
# got: '599'
# expected: '200'
not ok 5 - client 3: looks good

# Failed test 'client 3: looks good'
# at t/13-pre-fork.t line 26.
# undef
# doesn't match '(?^:^Hello customer number 0x[0-9a-f]+$)'
not ok 6 - client 2: http success

# Failed test 'client 2: http success'
# at t/13-pre-fork.t line 25.
# got: '599'
# expected: '200'
not ok 7 - client 2: looks good

# Failed test 'client 2: looks good'
# at t/13-pre-fork.t line 26.
# undef
# doesn't match '(?^:^Hello customer number 0x[0-9a-f]+$)'
not ok 8 - client 1: http success

# Failed test 'client 1: http success'
# at t/13-pre-fork.t line 25.
# got: '599'
# expected: '200'
not ok 9 - client 1: looks good

# Failed test 'client 1: looks good'
# at t/13-pre-fork.t line 26.
# undef
# doesn't match '(?^:^Hello customer number 0x[0-9a-f]+$)'
ok 10 - killing
...
t/13-pre-fork.t (Wstat: 2048 Tests: 12 Failed: 8)
  Failed tests: 2-9
  Non-zero exit status: 8
  Parse errors: Bad plan. You planned 16 tests but ran 12.
Files=27, Tests=931, 19 wallclock secs ( 0.09 usr 0.02 sys + 2.23 cusr 0.39 csys = 2.73 CPU)
Result: FAIL
autopkgtest [14:01:45]: test autodep8-perl-build-deps: -----------------------]
autopkgtest [14:01:45]: test autodep8-perl-build-deps: - - - - - - - - - - results - - - - - - - - - -
autodep8-perl-build-deps FAIL non-zero exit status 1
...

[Balint Reczey (rbalint)]

Flaky in newer releases, too.