fix: update broken ginger-lib reference to HorizenOfficial repository

[Galoretka]

Update the reference link in cubic_extension.rs from the deprecated
ZencashOfficial/ginger-lib repository to the current HorizenOfficial/ginger-lib
repository. The ginger-lib project was moved when Zencash rebranded to Horizen.

• Replace broken link: https://github.com/ZencashOfficial/ginger-lib/blob/development/r1cs/gadgets/std/src/fields/fp3.rs
• With working link: https://github.com/HorizenOfficial/ginger-lib/blob/master/r1cs/gadgets/std/src/fields/fp3.rs

This fixes the reference to the original implementation that was adapted for
the cubic extension field arithmetic in arkworks.