chore(ci): use --warn unsound in cargo audit

Author: hiltontj

.circleci/config.yml

@@ -271,8 +271,10 @@ jobs:
           command: cargo install cargo-deny --locked
       - run:
           name: cargo-deny Checks
-          command: cargo deny check -s
-
+          # `--warn unsound` downgrades RustSec `informational = "unsound"`
+          # advisories to warnings, they flag API soundness concerns, not
+          # exploitable vulnerabilities, so we don't want them to fail CI.
+          command: cargo deny check -s --warn unsound
   doc:
     docker:
       - image: quay.io/influxdb/rust:ci