Update CI

Author: GnomedDev

.github/workflows/rust.yml

@@ -40,8 +40,8 @@ jobs:
       run: cargo build --features=malloc_size_of --verbose
     - name: Run tests
       run: cargo test --verbose
-    - name: Run tests
-      run: cargo test --verbose
+    - name: Run tests (unstable)
+      run: cargo test --features=unstable --verbose
     - name: Run tests (serde)
       run: cargo test --features=serde --verbose
     - name: Run tests (gecko-ffi)