hreflang detection seems have issues

### FAQ

- [X] Yes, my issue is not about [variability](https://github.com/GoogleChrome/lighthouse/blob/master/docs/variability.md) or [throttling](https://github.com/GoogleChrome/lighthouse/blob/master/docs/throttling.md).
- [X] Yes, my issue is not about a specific accessibility audit (file with [axe-core](https://github.com/dequelabs/axe-core) instead).

### URL

https://vuepress-theme-hope.github.io/docs-demo/

### What happened?

### What did you expect?

### What have you tried?

zh-cn and zh-CN both doesn't work.

### How were you running Lighthouse?

web.dev

### Lighthouse Version

9.6.6

### Chrome Version

_No response_

### Node Version

_No response_

### OS

_No response_

### Relevant log output

_No response_

Start by reproducing the report at https://vuepress-theme-hope.github.io/docs-demo/ through web.dev using Lighthouse 9.6.6, and compare the hreflang detection with the expected screenshots. Verify whether both zh-cn and zh-CN are recognized; done means the reported hreflang values are detected as expected.

Written by the indexing model from the issue text.