Fix warning about offline banner on dashboard

[itsmeichigo]

Closes WOOMOB-1679

Description

When a device goes offline, we're showing offline banner on views that show cached data. Since iOS 26, we got a warning when showing the offline banner through navigation controller delegate to hosting controller of SwiftUI views:

This PR fixes this issue on the dashboard (My Store tab) by removing the shouldShowOfflineBanner computed variable from the hosting controller and add the offline banner to the SwiftUI view manually instead.

Test Steps

• Since network detection does not work properly on simulator, please build and run the app on a physical device instead.
• Disconnect the Internet connection.
• Confirm that the offline banner is displayed on the My Store screen.
• Confirm that there's no warning about the banner in Xcode.

Screenshots

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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 23.7. 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.

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[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	pr16347-9f2124c
	Version	23.6
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	9f2124c
	Installation URL	1s0g5e003tpq0

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