Fix flaky navigation-frontend-interactivity e2e tests

[t-hamano]

Alternatives to #68643

What?

Trying to solve the flaky tests in navigation-frontend-interactivity.spec.js:

• [Flaky Test] submenu click on the arrow interactions #61884
• [Flaky Test] Overlay menu interactions in Safari (@webkit) #55816
• [Flaky Test] page-list submenu user interactions #51348

How?

As mentioned in this comment, this may be because the canvas loader disappears very early. As a fallback, wait for the editor canvas instead of the canvas loader.

Testing Instructions

Let's see if the E2E tests are stable and successful.

[github-actions]

Flaky tests detected in 7419d61.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/12780055700
📝 Reported issues:

• [Flaky Test] Redirection after template creation #60678 in /test/e2e/specs/site-editor/site-editor-url-navigation.spec.js

[github-actions]

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Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[Mamaduka]

Thank you, @t-hamano!

Let's give it a try. There are no failures in five runs.