Update Briar Headless
From its readme: This is a merge of two MRs with briar's master on Oct 10 2020, 20:00 UTC: * briar!1286 * briar!1287
From its readme: This is a merge of two MRs with briar's master on Oct 10 2020, 20:00 UTC: * briar!1286 * briar!1287