remove: step to checkout branch to sync to (#1048)

    // Open the repositories we'll be working with

    let smithy_rs_repo = Repository::open(&smithy_rs).context("couldn't open smithy-rs repo")?;

    let aws_sdk_repo = Repository::open(&aws_sdk).context("couldn't open aws-sdk-rust repo")?;

    // Check repo that we're going to be moving the code into to see what commit it was last synced with

    let last_synced_commit =

        eprintln!("There are no new commits to be applied, have a nice day.");

        return Ok(());

    }

    // `git checkout` the branch of `aws-sdk-rust` that we want to replay commits onto.

    // By default, this is the `next` branch.

    checkout_branch_to_sync_to(&aws_sdk_repo, branch).with_context(|| {

        format!(

            "couldn't checkout {} branch of aws-sdk-rust for syncing",

            branch,

        )

    })?;

    let total_number_of_commits = commit_revs.len();

    let number_of_commits_to_sync = max_commits_to_sync.min(total_number_of_commits);

    Ok(())

}

/// `git checkout` the branch of aws-sdk-rust that we want to mirror commits to (defaults to `next`).

fn checkout_branch_to_sync_to(aws_sdk_repo: &Repository, aws_sdk_branch: &str) -> Result<()> {

    aws_sdk_repo

        .find_remote("origin")?

        .fetch(&["main"], None, None)?;

    let (object, _) = aws_sdk_repo.revparse_ext(aws_sdk_branch).context(here!())?;

    aws_sdk_repo.checkout_tree(&object, None).context(here!())?;

    Ok(())

}

/// `git checkout` a commit from smithy-rs that we're going to mirror to aws-sdk-rust.

fn checkout_commit_to_sync_from(smithy_rs_repo: &Repository, commit: &Commit) -> Result<()> {

    let head = smithy_rs_repo