Hi! thank you very much!
yes you're absolutely free to use them for your minetest mod
I'm so sorry i forgot to put down the specific license, the most befitting one would be CC-by-sa!
Sorry to bug you after you already made an effort, but would you mind either linking to a specific version of the CC-BY-SA or setting the “Asset license” field in the “More Information” box?
You’re so close to getting it perfect that it seems a shame to leave that ambiguity.