Just assume it's all GPLv3 so it can only be used in compatible projects...we only added CC-BY-SA to cover our backs since SuperTuxKart repository says it uses such licenses for assets but isn't clear about which asset is covered by which license...just remember to cite CC-BY-SA license along with GPLv3 when using it for your own projects...
Found Correct License: GPLv3 https://creativecommons.org/share-your-work/licensing-considerations/com...
Just assume it's all GPLv3 so it can only be used in compatible projects...we only added CC-BY-SA to cover our backs since SuperTuxKart repository says it uses such licenses for assets but isn't clear about which asset is covered by which license...just remember to cite CC-BY-SA license along with GPLv3 when using it for your own projects...