Function verify_tag 

pub fn verify_tag(
    git: &Repository,
    trust_root: Oid,
    shadow_policy: Option<&[u8]>,
    tag_name: &str,
    vresults: &mut VerificationResult,
    keep_going: bool,
    output: impl Output,
    cache: &mut VerificationCache,
    quiet: bool,
    verbose: bool,
) -> Result<()>