False positive: go/zipslip when `filepath.IsLocal` is already used

go/zipslip was detected, but the case was already protected by `filepath.IsLocal`.

Code example:

```go
r := tar.NewReader(bytes.NewReader(data))
for {
hdr, err := r.Next()
if err != nil {
if errors.Is(err, io.EOF) {
break // End of archive.
}
return fmt.Errorf("failed to read next tar entry: %v", err)
}
name := hdr.Name
if !filepath.IsLocal(name) {
continue
}
if hdr.FileInfo().IsDir() {
continue
}
// ... Make files/dirs based on name.
```

https://github.com/microsoft/go-infra/blob/7d114900fe9286d0fa400d02c6c5034b439d955b/gitcmd/gitcmd.go#L89-L125

https://github.com/microsoft/go-infra/security/code-scanning/4

> [IsLocal](https://pkg.go.dev/path/filepath#IsLocal) (added in go1.20) reports whether path, using lexical analysis only, has all of these properties:
>
> * is within the subtree rooted at the directory in which path is evaluated
> * is not an absolute path
> * is not empty
> * on Windows, is not a reserved name such as "NUL"
>
> If IsLocal(path) returns true, then Join(base, path) will always produce a path contained within base and Clean(path) will always produce an unrooted path with no ".." path elements.
>
> IsLocal is a purely lexical operation. In particular, it does not account for the effect of any symbolic links that may exist in the filesystem.

https://pkg.go.dev/archive/tar#Reader.Next mentions `IsLocal` as the way Go may automatically prevent zipslip:

> If Next encounters a non-local name (as defined by [filepath.IsLocal](https://pkg.go.dev/path/filepath#IsLocal)) and the GODEBUG environment variable contains `tarinsecurepath=0`, Next returns the header with an [ErrInsecurePath](https://pkg.go.dev/archive/tar#ErrInsecurePath) error. A future version of Go may introduce this behavior by default. Programs that want to accept non-local names can ignore the [ErrInsecurePath](https://pkg.go.dev/archive/tar#ErrInsecurePath) error and use the returned header.

---

I found an existing issue about go/zipslip, but it's about looking inside a func, not `IsLocal`:

* https://github.com/github/codeql/issues/17573

Start with the linked gitcmd.go lines 89-125 and the go/zipslip alert, then compare the filepath.IsLocal guard with the query's detection logic. Review issue 17573 for related context. Done means this protected case is no longer reported without suppressing genuine zipslip findings.

Scritto dal modello di indicizzazione a partire dal testo della issue.