Test assets cause Unity Editor stuck and huge gc when save asset

[chenquanjun]

When save a prefab, it will load all the ConfigGraph assets include test assets in "AssetGraph/Tests/Editor/Graphs/". It stuck editor and cause huge gc.

https://github.com/Unity-Technologies/AssetGraph/blob/e70a1be930b634ada9f97a79f1efb2599598bfc6/Editor/System/Model/V2/Settings.cs#L31

https://github.com/Unity-Technologies/AssetGraph/blob/e70a1be930b634ada9f97a79f1efb2599598bfc6/Editor/System/Core/AssetGraphPostprocessor.cs#L144-L153