CI: treat cargo clippy warning as error

Signed-off-by: Gris Ge <fge@redhat.com>

Author: cathay4t

.github/workflows/clippy-rustfmt.yml

@@ -28,4 +28,4 @@ jobs:
         run: cargo fmt --all -- --check
 
       - name: clippy
-        run: cargo clippy
+        run: cargo clippy -- -D warnings