[Maintenance] Update secp256k1-zkp to a more recent commit hash

[kdmukai]

Current dependency pulls in a commit hash that's over two years old.

https://github.com/BlockstreamResearch/secp256k1-zkp/commits/d9560e0af78d9059bba0c4845a310387abfa4e5e/

Would have to recompile the included binaries. Have not yet investigated if there are any breaking changes in the function names/args. May need to update the pure python implementation if anything would now be out of sync.