Baseline path should be normalized

[jneuff]

I don't understand how I can use the template that other issues seem to be using. I'll try to follow it manually.

• I'm submitting a bug report
• What is the current behavior?
  detect-secrets-hook does not scan for secrets in the provided baseline file. But this only works if the baseline path is provided in a certain way. E.g. git ls-files -z | xargs -0 detect-secrets-hook --json --baseline secrets.baseline works as expected. But git ls-files -z | xargs -0 detect-secrets-hook --json --baseline ./secrets.baseline will report secret findings in the secrets.baseline file itself, i.e.:

{
  "version": "1.5.0",
  "plugins_used": [..],
  "filters_used": [..],
   "results": {
    "secrets.baseline": [
      {
        "type": "Hex High Entropy String",
        "filename": "secrets.baseline",
        "hashed_secret": "7f1d53f684cf5b3fa755e815eb7648df53d04965",
        "is_verified": false,
        "line_number": 130
      }]
}

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem.
  As outlined above:

1. Create a baseline for a repo with findings. detect-secrets scan > secrets.baseline
2. Stage the baseline. git add secrets.baseline
3. Run the hook on that repo, passing the baseline with ./ as path prefix. git ls-files -z | xargs -0 detect-secrets-hook --json --baseline ./secrets.baseline
   - What is the expected behavior?
   The provided baseline file is not scanned, irrespective of how its path is referenced when calling detect-secrets-hook. That is the path to the baseline file should be normalized internally.

• What is the motivation / use case for changing the behavior?
  The current behavior is clearly a bug.

• Please tell us about your environment:
  detect-secrets Version: 1.5.0
  OS Version: Fedora 40 and Python Version: 3.10
  and
  OS Version: macOS ?? and Python Version ?? (detect-secrets 1.5.0 Installed via brew)