[Serve] Minor fix to replica shutdown

[simon-mo]

Signed-off-by: simon-mo [email protected]

Why are these changes needed?

Otherwise it throws

(ServeReplica:MyFastAPIDeployment pid=63096)   File "/Users/xmo/Desktop/ray/ray/python/ray/serve/_private/replica.py", line 529, in prepare_for_shutdown
(ServeReplica:MyFastAPIDeployment pid=63096)     del self.callable.__del__
(ServeReplica:MyFastAPIDeployment pid=63096) AttributeError: __del__

in the background. This is only caught because Ray Core was logging uncaught exception. This doesn't impact the normal teardown process, it only happens during FastAPI integration stack because that's the class that has the del attribute.

Related issue number

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• 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
  • Unit tests
  • Release tests
  • This PR is not tested :(

[edoakes]

@simon-mo this does not need to be cherry-picked because the relevant Ray core change is not cherry-picked, right?

[simon-mo]

Yup. We just need this in master.