[BUG] recover_sub_pool may raises RuntimeError: dictionary changed size during iteration

[codingl2k1]

Describe the bug

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Traceback (most recent call last):
  File "/Users/codingl2k1/.pyenv/versions/3.11.4/lib/python3.11/site-packages/xoscar/backends/pool.py", line 1402, in monitor_sub_pools
    await self.recover_sub_pool(address)
  File "/Users/codingl2k1/.pyenv/versions/3.11.4/lib/python3.11/site-packages/xoscar/backends/indigen/pool.py", line 329, in recover_sub_pool
    for _, message in self._allocated_actors[address].values():
RuntimeError: dictionary changed size during iteration

To Reproduce

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1. Your Python version 3.11.4
2. The version of Xoscar you use
3. Versions of crucial packages, such as numpy, scipy and pandas
4. Full stack of the error.
5. Minimized code to reproduce the error.

Expected behavior

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Additional context

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