Fix accessibility workflow DRb socket failure in CI

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What are you trying to accomplish?

Accessibility workflow failing in CI with Errno::ENOENT: No such file or directory - connect(2) for /tmp/druby2775.0. DRb Unix socket communication between parallel test workers fails in containerized CI environment with Ruby 3.4.

Change: Remove parallelize workers: 4 from test/accessibility_test.rb.

Tests now run serially, eliminating DRb dependency. No functional impact—all tests execute identically, just sequentially rather than in parallel.

Screenshots

N/A - CI infrastructure change only

Integration

List the issues that this change affects.

Job ID: 61779942020

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

Rationale: Removes one line. Tests run identically but serially. Pattern matches other system tests in repo that don't use parallelization.

What approach did you choose and why?

Parallel test execution via parallelize workers: 4 uses DRb with Unix sockets for IPC. Known failure mode in CI environments—socket files can't be created/accessed reliably in containers.

Alternatives considered:

• Configure socket directory: Complex, non-portable across CI environments
• Use threads instead of processes: Requires larger refactor, thread safety concerns
• Debug DRb initialization: Addresses symptom, not root cause

Serial execution is simplest fix. Test runtime increase acceptable for CI environment with 8-core runner.

Anything you want to highlight for special attention from reviewers?

None. Single-line deletion, pattern used throughout codebase.

Accessibility

N/A - Test infrastructure change only, no UI impact

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

Take a look at the What we look for in reviews section of the contributing guidelines for more information on how we review PRs.

Original prompt

Fix the failing GitHub Actions workflow Accessibility
Analyze the workflow logs, identify the root cause of the failure, and implement a fix.
Job ID: 61779942020
Job URL: https://github.com/primer/view_components/actions/runs/21451142941/job/61779942020

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