Use -D warnings instead of deny-warnings feature.

.github/workflows/clippy.yml

@@ -25,6 +25,7 @@ env:
   CARGO_TARGET_DIR: '${{ github.workspace }}/target'
   NO_FMT_TEST: 1
   CARGO_INCREMENTAL: 0
+  RUSTFLAGS: -D warnings
 
 concurrency:
   # For a given workflow, if we push to the same PR, cancel all previous builds on that PR.
@@ -47,25 +48,25 @@ jobs:
 
     # Run
     - name: Build
-      run: cargo build --tests --features deny-warnings,internal
+      run: cargo build --tests --features internal
 
     - name: Test
-      run: cargo test --features deny-warnings,internal
+      run: cargo test --features internal
 
     - name: Test clippy_lints
-      run: cargo test --features deny-warnings,internal
+      run: cargo test --features internal
       working-directory: clippy_lints
 
     - name: Test clippy_utils
-      run: cargo test --features deny-warnings
+      run: cargo test
       working-directory: clippy_utils
 
     - name: Test rustc_tools_util
-      run: cargo test --features deny-warnings
+      run: cargo test
       working-directory: rustc_tools_util
 
     - name: Test clippy_dev
-      run: cargo test --features deny-warnings
+      run: cargo test
       working-directory: clippy_dev
 
     - name: Test clippy-driver