Disallow compile warnings in CI

Co-authored-by: Shahar "Dawn" Or <[email protected]>

Author: warren2k

.github/workflows/ci.yml

@@ -35,7 +35,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust }}
-      - run: cargo check ${{ matrix.features }}
+      - run: RUSTFLAGS="--deny warnings" cargo check ${{ matrix.features }}
 
   test:
     name: test