test(port_std): add #![feature(const_trait_impl)] to the benchmark test

Fixes it failing to compile.

Author: yvt

.github/workflows/ci.yml

@@ -156,6 +156,13 @@ jobs:
           args: --workspace -- ${{ env.testflags }}
         env:
           RUST_LOG: debug
+      - name: Test (-p r3_port_std --benches)
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: -p r3_port_std --benches -- ${{ env.testflags }}
+        env:
+          RUST_LOG: debug
 
   # Run tests on the host system with a subset of optional features enabled
   test-hosted-subset:

src/r3_port_std/benches/test_suite.rs

@@ -1,5 +1,6 @@
 //! Runs test cases defined in `r3_test_suite`.
 #![feature(const_refs_to_cell)]
+#![feature(const_trait_impl)]
 #![feature(const_mut_refs)]
 #![feature(slice_ptr_len)]
 #![feature(never_type)]