Support custom buildTypes?

[arianvp]

I'm trying to upload a SLSA predicate with a custom buildType

https://github.com/arianvp/nix-attest/blob/86781ad55047cefbe3ae8ea8fd2fab838aedc36b/hook.sh#L59
https://github.com/arianvp/nix-attest/blob/86781ad55047cefbe3ae8ea8fd2fab838aedc36b/.github/workflows/ci.yml#L68

However during upload I get an error:

https://github.com/arianvp/nix-attest/actions/runs/12681357992/job/35344912224

Error: Error: Failed to persist attestation: Invalid Argument - unsupported build type: https://nixos.org/build/v1 - https://docs.github.com/rest/repos/repos#create-an-attestation

however nowhere is documented what build types are supported. Furthermore It would be great if custom build types are allowed just like custom predicate types

[bdehamer]

We are working to expand support for new predicate types and custom build types for the SLSA provenance predicate type. At the moment, the only build type supported for the SLSA provenance predicate is "https://github.com/slsa-framework/github-actions-buildtypes/tree/main/workflow/v1"