test: run CI on Windows and macOS

[kilisamemarisaaa]

What

Exercise morgan's test suite on Windows and macOS in CI, while preserving the existing Ubuntu/nvm matrix for historical Node.js versions.

Why

The current workflow only runs on ubuntu-latest. Adding native Windows and macOS coverage follows the cross-platform CI pattern already merged in expressjs/multer#1464 and proposed in expressjs/body-parser#759.

Changes

• Add a test-cross-platform job using actions/setup-node.
• Run Node.js 10.x–26.x on windows-latest; Node.js 10.x–21.x remain informational until measured.
• Run Node.js 16.x–26.x on macos-latest; 16.x–21.x are informational and 22.x+ are required checks.
• Keep the existing test job unchanged so the historical Node.js 0.8–26.x Ubuntu/nvm coverage and existing check name remain intact.
• Do not send cross-platform jobs to Coveralls, avoiding duplicate coverage uploads.

Verification

• Windows local baseline on Node.js v24.12.0: 93 passing and 6 passing.
• npm run lint passes locally.
• Workflow YAML parses successfully and git diff --check is clean.

As this is the first contribution from this fork to morgan, the workflow may require maintainer approval before GitHub Actions runs it.