Deny warnings in clippy check…

This is much better than denying warnings during build as even with warnings
present we can see the rest of the test suite failures at the same time.

.buildkite/pipeline.yml

@@ -1,6 +1,5 @@
 env:
   RUST_BACKTRACE: short
-  RUSTFLAGS: -D warnings
 
 steps:
   - label: "protobuf backward compatibility"

.github/workflows/rust.yml

@@ -27,9 +27,8 @@ jobs:
     steps:
       # Some of the tests allocate really sparse maps, so heuristic-based overcommit limits are not
       # appropriate here.
-      - run: |
-          cat /proc/meminfo || true
-          sudo sysctl vm.overcommit_memory=1 || true
+      # FIXME(#9634): remove this once the issue is resolved.
+      - run: sudo sysctl vm.overcommit_memory=1 || true
       - uses: actions/checkout@v2
       - uses: baptiste0928/cargo-install@21a18ba3bf4a184d1804e8b759930d3471b1c941
         with:
@@ -39,4 +38,4 @@ jobs:
           crate: cargo-deny
       - run: cargo nextest run --locked --workspace -p '*' --cargo-profile quick-release --profile ci ${{ matrix.flags }}
         env:
-          RUST_BACKTRACE: 1
+          RUST_BACKTRACE: short

test-utils/style/src/lib.rs

@@ -53,6 +53,7 @@ fn clippy() {
     cmd.args(&["clippy", "--all-targets", "--all-features", "--"]);
     cmd.args(&[
         "-Aclippy::all",
+        "-Dwarnings",
         "-Dclippy::clone_on_copy",
         "-Dclippy::correctness",
         "-Dclippy::derivable_impls",