Settings Sync: Fix Up Next settings

[bjtitus]

Fixes a minor issue when importing the Up Next setting. Previously this passed through the new update mechanism which would set the ModifiedDate to the current date, so this setting would be overwritten by the last device to import, which was not the original guidelines. We want any imported values to be assigned an epoch date (done in https://github.com/Automattic/pocket-casts-ios/pull/1616), not the current date, so they are clearly delineated from changed settings.

To test

• Change the return value of shouldEnableSyncedSettings in FeatureFlag.swift to false
• Subscribe to a podcast
• Enable "Add to Up Next" in the Podcast settings
• Enable the newSettingsStorage and settingsSync feature flags
• Restart the app
• Ensure your "Add to Up Next" setting remains the same

Checklist

• [x] I have considered if this change warrants user-facing release notes and have added them to CHANGELOG.md if necessary.
• [x] I have considered adding unit tests for my changes.
• [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 7.63. 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.

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