Add test and make sure the help center is not reparented.

[StevenDufresne]

Proposed Changes/Why are these changes being made?

We're getting the follow error in our logs:

Failed to execute 'removeChild' on 'Node': The node to be removed is not a child of this node.

I unfortunately can't reproduce in production but looking at the HelpCenter code, it appears like we could have a bug. As such, I've added a test that exposes the bug and added a fix.

Theory

The Help Center portal cleanup always called document.body.removeChild(portalParentRef.current), assuming the portal div was a direct child of document.body. If any code reparented the portal elsewhere in the DOM, unmounting would throw The node to be removed is not a child of this node because document.body was no longer its parent.

I need to be clear, I cannot reproduce and this is a theory :). I haven't been able to detach the help center from the document.body.

Considerations

I think the issue was introduced in this PR: 9e5e814

I'm not certain the change here is in the right direction. I'm hoping @wellyshen can provide guidance.

Testing Instructions

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-165483

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-165483&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-165483&env=a8c-for-agencies

Dashboard live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-165483&env=dashboard

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• help-center
• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug try/helpcenter-fix-reparenting-error on your sandbox.