[desrosj]

Backport of the runner update in #15518 to the 5.1 branch.

This changes the GitHub-hosted Ubuntu runners used by this branch's workflows from ubuntu-latest to ubuntu-26.04. GitHub is moving ubuntu-latest from 24.04 to 26.04 between 2026-10-19 and 2026-11-19, so this pins the version explicitly, matching trunk. A separate commit also pins windows-latest to windows-2025, matching trunk. windows-latest already points to windows-2025, so the Windows jobs are unchanged. The macOS jobs already use macos-15-intel, which is required because this branch uses Node.js 14, which never supported arm64.

The jobs defined in this branch's own workflow files are mostly housekeeping (Failed workflow tasks, the welcome message). The os matrix values passed to reusable workflows (PHPUnit, build process testing) are also updated. Jobs that call reusable workflows from trunk without an os input (JavaScript tests, E2E, coding standards, PHP compatibility) will move to 26.04 when #15518 is merged.

This branch does not use Playwright, so no dependency changes are needed.

Trac ticket: Core-66499

Use of AI Tools

Claude Code (Claude Opus 5.5) made the label changes, ran the fork-based test runs, and drafted this description. Draft PRs should be considered unverified and unreviewed by a human.

🤖 Generated with Claude Code

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