Function write_commit_object 

pub fn write_commit_object(
    repo: &Repository,
    data: &CommitData,
    sign_override: Option<bool>,
) -> Result<ObjectId>

Write a commit object to the ODB, honoring commit.gpgsign and sign_override.

Does not assign change ids; see prepare_commit_bytes.

Errors

Same as prepare_commit_bytes, plus object-database write failures.