Prevent schedule tests from making a plist file

[joshheald]

Description

This PR updates the unit tests to avoid creating BackgroundTaskScheduleTests.swift.plist on every test run

Test Steps

• Run unit tests
• Ensure BackgroundTaskScheduleTests.swift.plist is not in your working copy when they complete

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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]

	1 Warning
⚠️	This PR is assigned to the milestone 23.8. This milestone is due in less than 2 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

Generated by 🚫 Danger

[wpmobilebot]

📲 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	pr16404-fed061c
	Version	23.7
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	fed061c
	Installation URL	2gn1gmvvd3rh8

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

[iamgabrielma]

Works well!