test(playwright): check story has actually rendered before proceeding

[matthewgallo]

Contributes to #4688

I noticed that Cascade e2e avt test was passing even when it was being passed an incorrect story id which results in storybook's 404 page to display. This PR brings in similar changes @tay1orjones included in carbon-design-system/carbon#16132 after we chatted about this issue.

What did you change?

e2e/test-utils/storybook.js
packages/core/.storybook/preview.js
playwright.config.js

How did you test and verify your work?

• Ran playwright tests locally
  • With an incorrect story id, fails
  • And with a correct one, passes

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