tracing: move tracing instrumentation tests into tokio tests (#7007)

In #6112, tests for the tracing instrumentation were introduced. They
had to live in their own test crate under `tokio/tests` because the
`tracing-mock` crate that the tests use had not yet been published to
crates.io.

Now `tracing-mock` has been published to crates.io and so the separate
test crate and separate job to run it are no longer necessary. The
tracing instrumentation tests can be placed in with the other
integration tests in the `tokio` crate.

The tests themselves have also been updated to match the changes in the
`tracing-mock` API since the version which was being used.

.github/workflows/ci.yml

@@ -47,7 +47,6 @@ jobs:
       - test-workspace-all-features
       - test-integration-tests-per-feature
       - test-parking_lot
-      - test-tracing-instrumentation
       - valgrind
       - test-unstable
       - miri
@@ -246,34 +245,6 @@ jobs:
       - name: Check tests with all features enabled
         run: cargo check --workspace --all-features --tests
 
-  test-tracing-instrumentation:
-    # These tests use the as-yet unpublished `tracing-mock` crate to test the
-    # tracing instrumentation present in Tokio. As such they are placed in
-    # their own test crate outside of the workspace.
-    needs: basics
-    name: test tokio instrumentation
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: Install Rust ${{ env.rust_stable }}
-        uses: dtolnay/rust-toolchain@stable
-        with:
-          toolchain: ${{ env.rust_stable }}
-      - name: Install cargo-nextest
-        uses: taiki-e/install-action@v2
-        with:
-          tool: cargo-nextest
-
-      - uses: Swatinem/rust-cache@v2
-
-      - name: test tracing-instrumentation
-        run: |
-          set -euxo pipefail
-          cargo nextest run
-        working-directory: tokio/tests/tracing-instrumentation
-        env:
-          RUSTFLAGS: --cfg tokio_unstable -Dwarnings
-
   valgrind:
     name: valgrind
     needs: basics