ci: use release profile for loom tests

In both CONTRIBUTING.md, and in loom's own documentation, it is
recommended to run loom's tests with the --release profile, as they
execute many permutations of the same test and therefore compilation
time benefits are worthwhile.

In tokio-rs#7197 we see this with some individual tests taking over 60s to
complete.

Author: LloydW93

.github/workflows/ci.yml

@@ -842,7 +842,7 @@ jobs:
           toolchain: ${{ env.rust_stable }}
       - uses: Swatinem/rust-cache@v2
       - name: build --cfg loom
-        run: cargo test --no-run --lib --features full
+        run: cargo test --no-run --lib --release --features full
         working-directory: tokio
         env:
           RUSTFLAGS: --cfg loom --cfg tokio_unstable -Dwarnings