Fix cyclical dependency crash

[Nebby1999]

Fixes an issue caused by packages having cyclical dependencies.

Issue was originally caused by the behaviour described in this screenshot:

Steps to reproduce the crash:

1. Create a new unity project in version 2021.3.33f1
2. Install ThunderKit
3. Install the package "RoR2ImportExtensions" (latest version)
4. Disable all the importer steps except for "Install BepInEx"
5. Replace the method IEnumerable<PackageVersion> EnumerateDependencies(PackageVersion package, bool yield latestVersions) with this (It will force to download a version of RoR2BepInExPack with a cyclical dependency):

        IEnumerable<PackageVersion> EnumerateDependencies(PackageVersion package, bool yieldLatestVersions)
        {
            foreach (var dependency in package.dependencies)
            {
                string versionToUse = "latest";
                if(dependency.groupDependencyId == "RiskofThunder-RoR2BepInExPack")
                {
                    versionToUse = "1.37.0";
                }

                PackageGroup packageGroup = groupMap[dependency.groupDependencyId];
                var dep = yieldLatestVersions ? packageGroup[versionToUse] : dependency;

                foreach (var subDependency in EnumerateDependencies(dep, yieldLatestVersions))
                {
                    yield return subDependency;
                }
            }
            yield return package;
        }

6. Run the importer
7. The importer crashes due to a stack overflow exception during the dependency enumeration process.