Warning message for cmake code

When including a snippet of `CMakeLists.txt`, auto language discovery fails, so `lang:'cmake'` is necessary. But, when adding that, include-codeblock gives a warning:

```
warn: include-codeblock: unknown language `cmake`, use default
```

But the highlighting works fine.

透過包含 lang:'cmake' 的 CMakeLists.txt 程式碼片段來重現此警告，然後追蹤將 cmake 回報為未知的 include-codeblock 語言處理邏輯。警告消失且 CMake 語法高亮持續正常運作，即表示完成。

由索引模型根據 Issue 內容生成。