enable attributes feature

Signed-off-by: Yoshua Wuyts <[email protected]>

Author: yoshuawuyts

.github/workflows/ci.yml

@@ -62,7 +62,7 @@ jobs:
       uses: actions-rs/cargo@v1
       with:
         command: test
-        args: --all --features unstable
+        args: --all --features unstable attributes
 
   check_fmt_and_docs:
     name: Checking fmt and docs