Error When Importing YAML with {{}} Markup

Hello,

I’ve encountered an issue when importing YAML content that includes `{{}}`. This expression often appears in the GitHub Actions definitions documentation. It appears that HTML markup is being applied to the text within the {{}}, which causes rendering failures during nunjucks processing.

```
error: error while generating page "MY_DOCUMENT.md":
Template render error: (/home/USER_NAME/path/to/file/MY_DOCUMENT.md) [Line 62, Column 220]
unexpected token: <
at Object._prettifyError (/home/USER_NAME/PROJECT_DIR/node_modules/nunjucks/src/lib.js:32:11)
at Template.render (/home/USER_NAME/PROJECT_DIR/node_modules/nunjucks/src/environment.js:442:21)
at Environment.renderString (/home/USER_NAME/PROJECT_DIR/node_modules/nunjucks/src/environment.js:313:17)
at Promise.apply (/home/USER_NAME/PROJECT_DIR/node_modules/q/q.js:1185:26)
at Promise.promise.promiseDispatch (/home/USER_NAME/PROJECT_DIR/node_modules/q/q.js:808:41)
at /home/USER_NAME/PROJECT_DIR/node_modules/q/q.js:1411:14
at runSingle (/home/USER_NAME/PROJECT_DIR/node_modules/q/q.js:137:13)
at flush (/home/USER_NAME/PROJECT_DIR/node_modules/q/q.js:125:13)
at process.processTicksAndRejections (node:internal/process/task_queues:77:11)
```

**Steps to Reproduce:**

Import YAML content containing {{}} into the markdown, and set "YAML" as lang.
Then, convert this document using honkit such as `npx honkit pdf`

**Expected Behavior:** The content within {{}} should not have HTML markup applied, as it seems to interfere with the nunjucks rendering process.

**Actual Behavior:** HTML markup is applied to the content within {{}}, leading to rendering errors with nunjucks.

**Possible Solution:** A potential fix would be to adjust the import process to exclude the application of HTML markup to the content within {{}}. This should allow for successful rendering with nunjucks without encountering errors.

Thank you for looking into this issue. I believe addressing this could improve the experience.

Reproduce the failure by importing YAML containing {{}} and running npx honkit pdf. Trace the import path where HTML markup is applied before nunjucks processing. Done means the {{}} content remains unmarked and the document renders without the reported nunjucks error.

由索引模型根据 Issue 内容生成。