investigate how to void initialization of git repository for diff-java-tool

from https://github.com/checkstyle/test-configs/pull/192#issuecomment-2395218503

investigate why can not use path to git repo by "file://"

```
.github/workflows/project.yml
projects:
- name: diff-java-tool
scm: git
url: file:///home/runner/work/test-configs/test-configs/diff-java-tool
reference: main
```

Start with .github/workflows/project.yml and the referenced test-configs pull request discussion. Trace how the diff-java-tool project’s scm, url, and reference fields handle the file:// repository path; done means the cause is identified and the supported behavior or required configuration is clearly established.

Written by the indexing model from the issue text.