[#5985] Fix unit tests in nacos-core

[realJackSun]

fix #5985

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Follow this checklist to help us incorporate your contribution quickly and easily:

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• Format the pull request title like [ISSUE #123] Fix UnknownException when host config not exist. Each commit in the pull request should have a meaningful subject line and body.
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• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in test module.
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