feat: add output-file input for clean isort logging

[jmchilton]

Summary

Add optional output-file input to write isort output to a file in addition to stdout. This allows GitHub Actions workflows to capture structured isort output without cluttering job logs.

Changes

• New output-file input parameter (optional, default: empty string)
• Output written to file relative to repo root when specified
• Full stdout/log output preserved - file write is in addition to, not instead of
• Exit code and behavior unchanged

Rationale

When using isort with --check-only --diff in CI, output lands in GitHub Actions logs making them difficult to parse. This feature enables:

• Uploading output as artifacts for programmatic analysis
• Keeping logs clean while preserving full isort results
• Integration with downstream tools like LLM analysis pipelines

Example Usage

  - uses: isort/isort-action@v1
    with:
      output-file: isort-output.txt

  - uses: actions/upload-artifact@v4
    if: failure()
    with:
      name: isort report
      path: isort-output.txt