i18n: ensure metric names are untranslated

### FAQ

- [x] Yes, my issue is not about [variability](https://github.com/GoogleChrome/lighthouse/blob/main/docs/variability.md) or [throttling](https://github.com/GoogleChrome/lighthouse/blob/main/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).
- [x] Yes, my issue is not answered by [other FAQs](https://github.com/GoogleChrome/lighthouse#faq).

### URL

Site-agnostic (screenshots taken from local build, doublechecked on google.ca)

### What happened?

When generating reports in French, titles of all performance metrics remain in English.


When generating reports in Spanish, there is a similar issue - though some of the missing French translations are available in Spanish.


### What did you expect?

Translations that are supported should be complete.

### What have you tried?

_No response_

### How were you running Lighthouse?

CLI

### Lighthouse Version

12.3

### Chrome Version

_No response_

### Node Version

_No response_

### OS

_No response_

### Relevant log output

```sh

```