Backport GH-13617 for s390x (#13757)

[jackorp]

#13617

Same reason as #13757
But it was hit on Fedora's infra: https://koji.fedoraproject.org/koji/taskinfo?taskID=136229016

Failure can be seen in: https://kojipkgs.fedoraproject.org//work/tasks/9016/136229016/build.log
(Ephemeral log)

169) Error:
TestVariable#test_exivar_resize_with_compaction_stress:
RuntimeError: compaction doesn't work well on s390x. Omit the test in the caller.
    /builddir/build/BUILD/ruby-3.3.9-build/ruby-3.3.9/tool/lib/envutil.rb:249:in `under_gc_compact_stress'
    /builddir/build/BUILD/ruby-3.3.9-build/ruby-3.3.9/test/ruby/test_variable.rb:419:in `test_exivar_resize_with_compaction_stress'
Finished tests in 617.443873s, 43.1958 tests/s, 10265.6149 assertions/s.
26671 tests, 6338441 assertions, 0 failures, 1 errors, 168 skips
ruby -v: ruby 3.3.9 (2025-07-24 revision f5c772fc7c) [s390x-linux]

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Cherry-picked #13757