How to match files without a file extension?

I have a few use cases where I want to match files that have no file extension for example in case a passwd file has ended up in a codebase. I made this Devskim rule that works if I supply a file extension but if the filename is passwd without extension.

[
    {
        "name": "Detect /etc/passwd-like syntax",
        "id": "etcpasswdsyntax",
        "description": "Detects files containing /etc/passwd-like syntax (username:password:UID:GID:comment:home:shell).",
        "recommendation": "Review the file for sensitive data. Ensure it is not exposed or hardcoded in the project.",
        "severity": "BestPractice",
        "confidence": "high",
        "tags": ["security", "sensitive-data", "linux", "passwd"],
        "patterns": [
            {
                "pattern": "^[a-zA-Z0-9_]+:[x*!]?:[0-9]+:[0-9]+:[a-zA-Z0-9_,:/ -]+:[/a-zA-Z0-9_ -]+:[/a-zA-Z0-9_ -]+$",
                "type": "regex",
                "modifiers": ["m"],
                "_comment": "Matches /etc/passwd line syntax: user:pass:UID:GID:comment:home:shell"
            }
        ]
    }
]

For example on this file:

root:x:0:0:root:/root:/bin/bash
steve:x:1000:1000:Steve:/home/steve:/bin/bash
nobody:*:65534:65534:Nobody:/nonexistent:/usr/sbin/nologin