Bump nether from `d3f79e9` to `a03375c`

Bumps [nether](https://github.com/minetest-mods/nether) from `d3f79e9` to `a03375c`.
- [Release notes](https://github.com/minetest-mods/nether/releases)
- [Commits](https://github.com/minetest-mods/nether/compare/d3f79e961b591b322472fb7a378644ff144c5900...a03375c5a449855a9acaefe4ae691d34198a9d09)

nether @ a03375c5

-Subproject commit d3f79e961b591b322472fb7a378644ff144c5900
+Subproject commit a03375c5a449855a9acaefe4ae691d34198a9d09