Addon A11y: Avoid CSP issue

[Marklb]

Closes #24355

What I did

Ensure Ace result is a simple json object that doesn't contain named objects, because telejson will deserialize it in a way that violates: Content Security Policy directive: "script-src 'self' 'unsafe-inline'"

There may be a better way to handle this, such as just converting the CheckResult objects to a simple object, but I think all the Results object can be stringified, so I went with a simple naive approach: JSON.parse(JSON.stringify(result))

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

I don't know if there is a good way to automate testing this. Maybe adding the CSP to an e2e test that runs addon-a11y. I can try to do that, if it would work, but I am not sure how, yet.

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

1. Create a sandbox.
2. Create a .storybook/manager-head.html containing:

<meta
  http-equiv="Content-Security-Policy"
  content="script-src 'self' 'unsafe-inline'"
/>

3. Run the sandbox and check the devtools for a CSP error.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

[Marklb]

Anything else that needs to be done for this or done differently?

[valentinpalkovic]

Thanks @Marklb!