e2e: Fix random Form AI placeholders

[anomiex]

Proposed Changes

Update the test to match the different possible placeholders.

Why are these changes being made?

Automattic/jetpack#39482 changed the placeholder for the form AI assistant.

Testing Instructions

• Run tests, e.g. VIEWPORT_NAME="desktop" ATOMIC_VARIATION="default" TEST_ON_ATOMIC="true" JETPACK_TARGET="wpcom-deployment" yarn workspace wp-e2e-tests test test/e2e/specs/blocks/blocks__jetpack-forms.ts

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 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 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-120262

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-120262&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-120262&env=a8c-for-agencies

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[lhkowalski]

Fixed as expected.