Improve syncing of deselected chapters

[geekygecko]

Description

There was an issue in the sync process that would cause the deselect chapters to keep syncing. This was because the modified value wasn't set to null after it was synced, causing the new sync to send it again.

Testing Instructions

• Fresh install the app
• Create a new account
• Upgrade it to Plus
• Subscribe to a podcast with chapters for example Upgrade https://pca.st/upgrade
• Play an episode
• Open the full screen player and chapters tab
• Tap "Preselect chapters"
• Unselect a chapter and tap Done
• Open the Android Studio window "App Inspection" and the "Network Inspector" tab
• Back in the app tap the Profile tab -> refresh button
• Find the /sync/update call
• The request is encoded but you should be able to see the deselected_chapters being sent and an episode being returned in the response
• Wait a little while then tap the refresh button again
• ✅ Verify that the request is empty and doesn't send the episode with the deselected_chapters field. The response should also be empty.

Checklist

• [x] If this is a user-facing change, I have added an entry in CHANGELOG.md
• [x] Ensure the linter passes (./gradlew spotlessApply to automatically apply formatting/linting)
• [x] I have considered whether it makes sense to add tests for my changes
• [x] All strings that need to be localized are in modules/services/localization/src/main/res/values/strings.xml
• [x] Any jetpack compose components I added or changed are covered by compose previews
• [x] I have updated (or requested that someone edit) the spreadsheet to reflect any new or changed analytics.

[dangermattic]

	1 Warning
:warning:	This PR is assigned to the milestone 7.77 ❄️. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

Generated by :no_entry_sign: Danger

[wpmobilebot]

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

	App Name	📱 Mobile
	Build Type	debugProd
	Commit	78903eade107a736b9cff7e02aa3cb6521564bf6
	Direct Download	pocketcasts-app-prototype-build-pr3256-78903ea.apk

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

	App Name	🚗 Automotive
	Build Type	debugProd
	Commit	78903eade107a736b9cff7e02aa3cb6521564bf6
	Direct Download	pocketcasts-automotive-prototype-build-pr3256-78903ea.apk

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

	App Name	⌚ Wear
	Build Type	debugProd
	Commit	78903eade107a736b9cff7e02aa3cb6521564bf6
	Direct Download	pocketcasts-wear-prototype-build-pr3256-78903ea.apk