Flaky conformance test: paren-ambiguity gzip example has non-deterministic stderr ordering

[ewhauser]

Description

The conformance test TestConformance/bash/oils/paren-ambiguity.test.sh/((gzip_example_-_zdiff_package_-_#2337 is flaky due to non-deterministic stderr interleaving between concurrent gzip subprocesses.

The test file itself notes this at line 89-90:

The gzip failures here are incidental; their stderr interleaving differs across runtimes and hosts

Observed failure (CI Linux runner)

gbash stderr: "3: Bad file descriptor\ngzip: .gz: No such file or directory\ngzip: .gz: No such file or directory\n"
bash stderr:  "3: Bad file descriptor\ngzip: gzip: .gz: No such file or directory\n.gz: No such file or directory\n"

Expected behavior

The test should either ignore stderr comparison for this case or normalize the stderr ordering before comparison.

Reproduction

Passes locally on macOS but intermittently fails on CI (Linux). Observed in PR #683 CI run https://github.com/ewhauser/gbash/actions/runs/23420484096/job/68124356048