Fix/ray serve test state api usage (ray-project#56948)

## Why are these changes needed?

Fixes a unit test that was broken but not running in CI.

## Related issue number

Fixes ray-project#53478 

## Checks

- [y] I've signed off every commit(by using the -s flag, i.e., `git
commit -s`) in this PR.
- [y] I've run `scripts/format.sh` to lint the changes in this PR.
- [y] I've included any doc changes needed for
https://docs.ray.io/en/master/.
- [ ] I've added any new APIs to the API Reference. For example, if I
added a
method in Tune, I've added it in `doc/source/tune/api/` under the
           corresponding `.rst` file.
- [y] I've made sure the tests are passing. Note that there might be a
few flaky tests, see the recent failures at
https://flakey-tests.ray.io/.
- Testing Strategy
   - [y] Unit tests
   - [ ] Release tests
   - [ ] This PR is not tested :(

---------

Signed-off-by: Jason <jcarlson212@gmail.com>
Co-authored-by: Edward Oakes <ed.nmi.oakes@gmail.com>

Author: 2 people

python/ray/serve/tests/test_metrics.py

@@ -1082,7 +1082,7 @@ def f():
 
     serve.run(f.bind(), name="app")
     actors = list_actors(filters=[("state", "=", "ALIVE")])
-    class_names = {actor["class_name"] for actor in actors}
+    class_names = {actor.class_name for actor in actors}
     assert class_names.issuperset(
         {"ServeController", "ProxyActor", "ServeReplica:app:f"}
     )