[nix] Fix profile list index for raw flakes (#1471)

## Summary

ProfileListIndex was broken for raw flakes. This would break `devbox
update`

I could have left the `return -1, errors.Wrap(nix.ErrPackageNotFound,
args.Package.String())` inside the if statement, but it seems safer to
just to attempt the slow matching instead of returning an error and only
returning an error after all matching fails.

Blame PR: #1422

## How was it tested?

```bash
devbox add github:F1bonacc1/process-compose/v0.43.1
devbox update
```

Author: mikeland73

internal/nix/nixprofile/profile.go

@@ -127,14 +127,15 @@ func ProfileListIndex(args *ProfileListIndexArgs) (int, error) {
 		return -1, err
 	}
 
-	if !inCache {
+	if !inCache && args.Package.IsDevboxPackage() {
 		// This is an optimization for happy path when packages are added by flake reference. A resolved devbox
 		// package *which was added by flake reference* (not by store path) should match the unlockedReference
 		// of an existing profile item.
 		ref, err := args.Package.NormalizedDevboxPackageReference()
 		if err != nil {
 			return -1, errors.Wrapf(err, "failed to get installable for %s", args.Package.String())
 		}
+
 		for _, item := range items {
 			if ref == item.unlockedReference {
 				return item.index, nil