Enable clippy on tests and examples

Might as well run the lints on our tests and examples. When I first
started doing this cleanup, I thought this was the default, but I must
have run `cargo clippy --all-targets` at some point in there.

.github/workflows/clippy.yml

@@ -23,4 +23,4 @@ jobs:
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          args: -- -D warnings
+          args: --tests --examples -- -D warnings