Enable type layout randomization in CI on nightly

Author: dtolnay

.github/workflows/ci.yml

@@ -31,6 +31,9 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{matrix.rust}}
+      - name: Enable type layout randomization
+        run: echo RUSTFLAGS=${RUSTFLAGS}\ -Zrandomize-layout >> $GITHUB_ENV
+        if: matrix.rust == 'nightly'
       - run: cargo test
 
   msrv: