Deny warnings

Author: wks

.github/workflows/style_check.yml

@@ -5,11 +5,20 @@ jobs:
   header_check:
     runs-on: ubuntu-latest
     name: Check code style
+    env:
+      # Deny warnings in cargo clippy:
+      RUSTFLAGS: -D warnings
     steps:
       - uses: actions/checkout@v4
-      - name: Rust lints using Clippy
+      - name: Rust lints using Clippy (debug)
         working-directory: gc/mmtk
         run: cargo clippy
+      - name: Rust lints using Clippy (tests)
+        working-directory: gc/mmtk
+        run: cargo clippy --tests
+      - name: Rust lints using Clippy (release)
+        working-directory: gc/mmtk
+        run: cargo clippy --release
       - name: Rust code format check
         working-directory: gc/mmtk
         run: cargo fmt --check