fix: CallKit crashes when in background - WPB-17848

[github-actions]

This PR was automatically cherry-picked based on the following PR:

• fix: CallKit crashes when in background - WPB-17848 #3060

Original PR description:

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WPB-17848 [iOS] App crashes in background when there are CallKit calls

Issue

Context: When incoming calls arrive in the background and they're handled with CallKit, app crashes.

Causes: Some changes were introduced recently in this PR where we replaced pushRetry and reportNewIncomingCall completionHandler versions of Apple's API with their async versions which appear to be broken as they're not called properly when waking up the app from the background.

It ends up crashing as since iOS 13:

if you fail to report a call to CallKit, the system will terminate your app.

..which is what we experienced when looking at the console.

Solution: As mentioned in the latest comments in this SO post and after testing with both versions (async vs. completionHandler), the issue was reproducible with the async version and appeared to work properly with the completionHandler one.
Solution is to revert these changes to make sure we use the completionHandler API versions as before, thus properly report the call and avoid crashing.

Testing

Tested internally on both async / completionHandler versions, issue was reproducible on the async version, not the completionHandler one.

Checklist

• Title contains a reference JIRA issue number like [WPB-XXX].
• Description is filled and free of optional paragraphs.
• Adds/updates automated tests.

[github-actions]

Test Results

3 142 tests   3 116 ✅  4m 3s ⏱️
  441 suites     26 💤
    2 files        0 ❌

Results for commit a17bf38.

[datadog-wireapp]

Datadog Report

Branch report: fix/crash-incoming-calls-when-in-background-cherry-pick
Commit report: eb38e59
Test service: wire-ios-mono

✅ 0 Failed, 3116 Passed, 26 Skipped, 2m 3.85s Total Time