Exclude storybook from scanning

What does this MR do and why?

A fairly large amount of our dependency scanner findings are in the storybook/yarn.lock file, which is used only in development.

We used to include those files in our production images even though they weren't used, but as of Remove storybook directories (gitlab-org/build/CNG!2142 - merged) we don't ship this anymore so it's now safe to stop scanning them.

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

MR acceptance checklist

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How to set up and validate locally

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