fix cargo test arguments on ci

Author: k-nasa

.github/workflows/ci.yml

@@ -63,7 +63,7 @@ jobs:
       uses: actions-rs/cargo@v1
       with:
         command: test
-        args: --all --features unstable attributes
+        args: --all --features "unstable attributes"
 
   check_fmt_and_docs:
     name: Checking fmt and docs