Fix incorrectly terminated background task

[kean]

The app currently prints the following error message when the background task expiration handler is called:

2023-08-04 10:50:17.838280-0400 Jetpack[60050:4787549] [BackgroundTask] Background task still not 
ended after expiration handlers were called: <_UIBackgroundTaskInfo: 0x15523b7e0>: taskID = 30, 
taskName = Called by Jetpack, from $s9WordPress0aB11AppDelegateC29applicationDidEnterBackgroundyySo13UIApplicationCFTo, 
creationTime = 401007 (elapsed = 26). This app will likely be terminated by the system. 
Call UIApplication.endBackgroundTask(_:) to avoid this.

The reason is that the app doesn't end the task immediately on termination. The expiration handler is already called on the main queue, so there is no need to dispatch it.

This may be one of the reasons of WatchdogTermination events.

To test:

• Put the app in the background
• Verify that the error messages is no longer called

Regression Notes

1. Potential unintended areas of impact: background tasks
2. What I did to test those areas of impact (or what existing automated tests I relied on): manual test
3. What automated tests I added (or what prevented me from doing so): n/a

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

UI Changes testing checklist:

• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[peril-wordpress-mobile]

	Warnings
⚠️	PR is not assigned to a milestone.

Generated by 🚫 dangerJS

[kean]

It's unlikely it's the reason for terminations, but better safe than sorry.

[salimbraksa]

❓ I agree with the removal of DispatchQueue.main.async, but do you have an idea why it was added in the first place? Maybe it was added to fix some bug. But even in that case, the ideal solution shouldn't be DispatchQueue.main.async.

[kean]

I tried to check the history, but this code has been moved around a bit.

Based on the comment ("synchronize on the main thread"), this async is unnecessary because the expiration handler is already called on the main thread:

The system calls the handler synchronously on the main thread, blocking the app’s suspension momentarily.
From https://developer.apple.com/documentation/uikit/uiapplication/1623031-beginbackgroundtaskwithexpiratio

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr21254-bc73fc4
	Version	22.9
	Bundle ID	org.wordpress.alpha
	Commit	bc73fc4
	App Center Build	WPiOS - One-Offs #6617

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr21254-bc73fc4
	Version	22.9
	Bundle ID	com.jetpack.alpha
	Commit	bc73fc4
	App Center Build	jetpack-installable-builds #5652

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[salimbraksa]

LGTM!