Revert "chore: disable warnings in old CI (#4691)"

This reverts commit b24df49a9d so we can
merge the CHANGELOG changes in #4691 into master.

.github/workflows/ci.yml

@@ -7,6 +7,7 @@ on:
 name: CI
 
 env:
+  RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: 1
   nightly: nightly-2021-10-25
   minrust: 1.45.2
@@ -64,6 +65,11 @@ jobs:
         run: cargo hack test --each-feature
         working-directory: tests-integration
 
+      # Run macro build tests
+      - name: test tests-build --each-feature
+        run: cargo hack test --each-feature
+        working-directory: tests-build
+
       # Build benchmarks. Run of benchmarks is done by bench.yml workflow.
       - name: build benches
         run: cargo build --benches
@@ -123,7 +129,7 @@ jobs:
         run: cargo test --all-features
         working-directory: tokio
         env:
-          RUSTFLAGS: --cfg tokio_unstable
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 
   miri:
     name: miri
@@ -207,7 +213,7 @@ jobs:
       - name: check --each-feature --unstable
         run: cargo hack check --all --each-feature -Z avoid-dev-deps
         env:
-          RUSTFLAGS: --cfg tokio_unstable
+          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 
   minrust:
     name: minrust
@@ -292,7 +298,7 @@ jobs:
         run: cargo doc --lib --no-deps --all-features --document-private-items
         env:
           RUSTFLAGS: --cfg docsrs
-          RUSTDOCFLAGS: --cfg docsrs
+          RUSTDOCFLAGS: --cfg docsrs -Dwarnings
 
   loom-compile:
     name: build loom tests
@@ -306,7 +312,7 @@ jobs:
         run: cargo test --no-run --lib --features full
         working-directory: tokio
         env:
-          RUSTFLAGS: --cfg loom --cfg tokio_unstable
+          RUSTFLAGS: --cfg loom --cfg tokio_unstable -Dwarnings
 
   check-readme:
     name: Check README

.github/workflows/loom.yml

@@ -8,6 +8,7 @@ on:
 name: Loom
 
 env:
+  RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: 1
 
 jobs:
@@ -34,6 +35,6 @@ jobs:
         run: cargo test --lib --release --features full -- --nocapture $SCOPE
         working-directory: tokio
         env:
-          RUSTFLAGS: --cfg loom --cfg tokio_unstable
+          RUSTFLAGS: --cfg loom --cfg tokio_unstable -Dwarnings
           LOOM_MAX_PREEMPTIONS: 2
           SCOPE: ${{ matrix.scope }}