Invoke clippy better for tests

See rust-lang/rust-clippy#1436 (comment)

Author: kulp

.github/workflows/bindgen.yml

@@ -35,7 +35,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: -- --cfg test
+          args: --tests
 
   msrv:
     runs-on: ubuntu-latest