fix: properly handle go.mod files with no dependencies

[Strum355]

Description

If go.mod file is empty go mod graph would return only one line (containing @go that we filter out), which would cause an exception when trying to determine the root module. Instead we can use go mod edit -json to get the root module from the following output:

{
        "Module": {
                "Path": "github.com/sample/empty-module"
        },
        "Go": "1.24",
        "Require": null,
        "Exclude": null,
        "Replace": null,
        "Retract": null,
        "Tool": null
}

Checklist

• I have followed this repository's contributing guidelines.
• I will adhere to the project's code of conduct.

Additional information

Anything else?