Function sync_proposal 

fn sync_proposal<G: GitHistory + GitRefs + ProposalGit, B: AssetBuilder>(
    git: &G,
    builder: &B,
    state: &ReleaseState,
    request: ConfiguredProposal<'_>,
    expectation: Expectation<'_>,
) -> Result<Synchronized, ProposalError>

Discover configured units, analyze changes, and synchronize the maintained release branch using the evaluated release policy. expectation comes from the open proposal pull request.