chore: add a changelog entry

changes/v5.0.15/fix-9749-en.md

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+In some cases search APIs could respond with an incorrect `count` value in the metadata, that is usually much bigger than expected, this is now fixed.

changes/v5.0.15/fix-9749-zh.md

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+在某些情况下，搜索 API 可能会在元数据中响应不正确的 `count` 值，这通常比预期的要大得多，现在已经修复了。