fix: Prevent JSON SyntaxError on non-2xx API responses

[sentry]

The browser extension was encountering SyntaxError: Unexpected token 'F', "Forbidden" is not valid JSON when making API calls to Codecov. This occurred because the Codecov API returns a plain-text "Forbidden" message with a 403 status code when authentication or authorization fails. The fetchCommitReport, fetchPRComparison, listFlags, and listComponents methods in src/service.ts were unconditionally calling response.json() on these non-JSON responses, leading to the error.

This fix modifies these four methods to check response.ok before attempting to parse the response as JSON. If response.ok is false, the methods now return { ok: false, data: null }, preventing the SyntaxError and allowing upstream callers (which already handle ok: false) to gracefully manage the API error.

Fixes BROWSER-EXTENSION-RM

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}

[codecov]

Bundle Report

Changes will increase total bundle size by 245 bytes (0.04%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
codecov-browser-extension-array-push	660.71kB	245 bytes (0.04%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: codecov-browser-extension-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
background.js	245 bytes	207.9kB	0.12%