.github/problemMatcher/blackWarning.json

{
    "problemMatcher": [
        {
            "owner": "black-warning",
            "severity": "warning",
            "pattern": [
                {
                    "regexp": "^(would reformat (.*))$",
                    "file": 2,
                    "message": 1
                }
            ]
        }
    ]
}