[Core] Only instantiate gcs channels on driver

[pcmoritz]

Why are these changes needed?

After https://github.com/ray-project/ray/pull/36293 is merged we can now fix this.

This fixes https://github.com/ray-project/ray/issues/36001 -- I can repro both the hanging and the fact that this PR fixes it on my mac laptop. The rationale for the fix is described in https://github.com/ray-project/ray/pull/36109#issuecomment-1577988403

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 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.
• [ ] 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 :(

[vitsai]

Is object spilling test timeout new?

[pcmoritz]

No, it has been flaking quite a bit, I'm re-running to make sure it didn't get more flaky :)