fix: etcd watch失败时，内存泄漏 #2919

[hauerwu]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• [x] Bugfix
• [ ] New feature provided
• [ ] Improve performance
• [ ] Backport patches

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Related issues

fix/resolve #2919

Checklist:

• [x ] Did you explain what problem does this PR solve? Or what new features have been added?
• [ ] Have you added corresponding test cases?
• [ ] Have you modified the corresponding document?
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[monkeyDluffy6017]

@nic-chen @bzp2010 please help to check