fix refcell borrow_mut error cause channel closed

[Millione]

13

[codecov[bot]]

Codecov Report

Patch coverage: 76.19% and project coverage change: +0.22 :tada:

Comparison is base (0324d16) 83.57% compared to head (414015a) 83.80%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #44 +/- ## ========================================== + Coverage 83.57% 83.80% +0.22% ========================================== Files 17 17 Lines 1924 1920 -4 ========================================== + Hits 1608 1609 +1 + Misses 316 311 -5 ``` | [Impacted Files](https://codecov.io/gh/al8n/stretto/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Al+Liu) | Coverage Δ | | |---|---|---| | [src/cache/async.rs](https://codecov.io/gh/al8n/stretto/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Al+Liu#diff-c3JjL2NhY2hlL2FzeW5jLnJz) | `85.39% <62.50%> (+0.08%)` | :arrow_up: | | [src/cache/sync.rs](https://codecov.io/gh/al8n/stretto/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Al+Liu#diff-c3JjL2NhY2hlL3N5bmMucnM=) | `86.54% <83.33%> (-0.36%)` | :arrow_down: | | [src/ttl.rs](https://codecov.io/gh/al8n/stretto/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Al+Liu#diff-c3JjL3R0bC5ycw==) | `81.70% <85.71%> (+5.04%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Al+Liu). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Al+Liu)

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