Make cachix builds from CI/CD match CLI/flake inputs

[juliankuners]

This pull request fixes the same kind of issue that I already observed and fixed in evm-semantics, kontrol, and more, see, e.g., evm-semantics#2739, evm-semantics#2745, and kontrol#1013.

The CI/CD pipeline for komet builds and publishes komet to the nix build cache k-framework-binary. In the respective GitHub action job, the nix derivation is built by cloning the repository and building the derivation locally. When building the nix project locally with a cloned git repository, nix does not include and consider empty submodule directories included by git for building the project. On the other hand, when the repository is referenced in a flake input or built by specifying a github URL in a nix CLI command, the empty submodule directories are included. This causes the package requested by kup, nix CLI, or nix flake inputs to not match the package built by CI/CD that is pushed to the build cache.

As a consequence, komet is built on the local machine instead of fetched from the binary cache.

This pull request fixes this issue such that the same version/hash of the derivation is always built for the cache and requested by flake inputs/CLI/kup. After merging this pull request, kup install komet will download komet from the nix build cache instead of building it locally.

[juliankuners]

I just tested this with the upstream branch from this pull request and can confirm that hashes now match.