Add RUSTFLAGS="-Dwarnings" env for Clippy job

Author: newpavlov

.github/workflows/workspace.yml

@@ -13,6 +13,8 @@ jobs:
   clippy:
     name: Clippy
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: "-Dwarnings"
     steps:
     - uses: actions/checkout@v3
     - uses: dtolnay/rust-toolchain@master