mixed-line-ending fails on Windows when operating on COMMIT_EDITMSG (--fix=lf) #1267

Summary

When committing on a Windows environment with mixed-line-ending configured with --fix=lf, the hook runs against COMMIT_EDITMSG, fixes the CRLF line endings to LF, and exits with code 1, aborting the commit.

Environment

• OS: Windows
• pre-commit version: 3.8.0
• pre-commit-hooks version: v6.0.0
• Git version: 2.50.1

Configuration (.pre-commit-config.yaml)

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v6.0.0
    hooks:
      - id: trailing-whitespace
        args: [--markdown-linebreak-ext=md]
      - id: end-of-file-fixer
      - id: mixed-line-ending
        args: [--fix=lf]
      - id: check-merge-conflict
      - id: check-added-large-files
        args: [--maxkb=500]
      - id: check-yaml
        args: [--unsafe]
      - id: forbid-submodules
      - id: check-executables-have-shebangs
      - id: check-shebang-scripts-are-executable

Expected Behavior

mixed-line-ending should either ignore COMMIT_EDITMSG by default or handle system-generated commit message files without failing the commit step on Windows.