fix: Update file path for fetching locales, to match mv3 folder struc…

…ture (#24983)

## **Description**

This fixes an error found in this comment
#24942 (comment)
"I get Fail to fetch when I switch languages."

This error is a result of the changes in
#23672

That PR has the following in the description:

> ...The manifest file sometimes references files using a path relative
to both the repo and the bundled extension (background.html and
popup.html) and sometimes it doesn't (inpage.js lives in the scripts
folder).
This PR makes the paths relative to the repo (and the bundled
extension).

We need to adjust the filepath for fetching these locales as well, which
this PR does

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## **Manual testing steps**

1. Go to the settings page and try to switch a language
2. The language should update successfully AND there should be no error
in the console
3. Reload the extension. The same language should be selected

## **Pre-merge author checklist**

- [x] I’ve followed [MetaMask Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

shared/modules/i18n.test.ts

@@ -281,7 +281,7 @@ describe('I18N Module', () => {
     it('returns json from locale file', async () => {
       const result = await fetchLocale(localeCodeMock);
       expect(result).toStrictEqual({
-        url: `./_locales/${localeCodeMock}/messages.json`,
+        url: `../_locales/${localeCodeMock}/messages.json`,
       });
     });
 

shared/modules/i18n.ts

@@ -91,7 +91,7 @@ export async function fetchLocale(
 ): Promise<I18NMessageDict> {
   try {
     const response = await fetchWithTimeout(
-      `./_locales/${localeCode}/messages.json`,
+      `../_locales/${localeCode}/messages.json`,
     );
     return await response.json();
   } catch (error) {