[ci] fix cargo hack test invocation

.github/workflows/ci.yml

@@ -61,4 +61,4 @@ jobs:
         # Note: you might think that we can also pass in `--exclude-all-features` here, but that
         # isn't the case because if you pass in a --example, it doesn't run doctests. The below
         # expression will run doctests as well.
-        run: cargo hack --feature-powerset
+        run: cargo hack test --feature-powerset