Configure cargo-deny fully

This adds more configuration to cargo-deny so that the output is not a
giant list of warnings hiding new entries.  Instead the config now
lists the things that would emit warnings.  It also adds -Dwarnings to
the CI job so that new warnings will be cleaned up: they can be added
to the config easily to fix the warnings.

.github/workflows/ci.yml

@@ -40,6 +40,8 @@ jobs:
       - uses: EmbarkStudios/cargo-deny-action@v1
         with:
           arguments: --all-features --workspace
+          command: check
+          command-arguments: "-Dwarnings"
 
   provider_database:
     name: Check provider database