fix(updateAvailable): stub async cacheRelease and fetchAndStore

[whomwah]

This pull request refactors the update checking logic in updateAvailableItem and its related helpers to use async/await instead of fire-and-forget promises. The main goal is to ensure that cache updates and fetch operations complete before proceeding, which improves reliability and testability. The tests have also been updated to reflect the new asynchronous behavior.

Refactoring to use async/await for update checks:

• Changed updateAvailableItem to be an async function and now awaits _internals.cacheRelease, ensuring that caching completes before continuing (src/helpers/updateAvailable.ts).
• Updated cacheRelease to be an async function and to await _internals.fetchAndStore, rather than calling it in a fire-and-forget manner, so that update checks are properly awaited (src/helpers/updateAvailable.ts).

Test updates for async changes:

• Modified all relevant tests to stub cacheRelease and fetchAndStore with async functions returning resolved promises, aligning with the new async behavior (src/helpers/updateAvailable.test.ts). [1] [2] [3] [4]
• Removed logic in tests that waited for fire-and-forget promises, since update checks are now awaited directly (src/helpers/updateAvailable.test.ts).

[whomwah]

🎉 This PR is included in version 1.11.3 🎉

The release is available on GitHub release

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