[core] Deflake and speed up test_gcs_fault_tolerance.py (#52743)

`test_gcs_fault_tolerance.py` is highly flaky, partially because it's
bumping up against the 300s
[timeout](https://buildkite.com/ray-project/postmerge/builds/9884#01968e57-2a5b-4334-a05a-cca770782c7b/180-1563).
Instead of increasing the timeout, reducing the runtime of the test.

- Remove unnecessary sleeps and use explicit signaling where possible.
- Combined two test cases for actor behavior into one (they were
redundant).

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

Author: edoakes