Flaky Jetpack E2E: when using AI Assistant block, validate only whether paragraph block exists.

[worldomonation]

Related to #80730, #81580.

Proposed Changes

This PR is a follow-up to #81580 and updates the expectation in light of a flakeout by ChatGPT noted in p1694596605435499-slack-CDLH4C1UZ.

There will still be an initial attempt to verify the keyword(s) are present in the post, but if that fails, the block flow will fall back to simply verifying whether a paragraph block exists.

Unfortunately, because there is no reliable way to tell what generated the paragraph block in the published post, it is not possible to further narrow the selector.

Testing Instructions

Ensure the following build configurations are passing:

• Calypso E2E (desktop)
• Jetpack E2E Simple (mobile)
• Jetpack E2E Simple (desktop)
• Jetpack E2E AT (desktop)

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md 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-ajp-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-80746

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-80746&env=jetpack

[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.

[dpasque]

This is for sure the right call -- thanks for leaving such a helpful comment in the code! 💛