Fix deadlock crash when updating UserDefaults

[itsmeichigo]

Closes WOOMOB-1524

Description

Steps to reproduce

Testing information

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[dangermattic]

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

	App Name	WooCommerce iOS Prototype
	Build Number	pr16256-e89461e
	Version	23.5
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	e89461e
	Installation URL	75gv38ebda9f8

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