build: exclude .storybook and scripts directories from coverage report

[tomdavies73]

Proposed behaviour

Excludes .storybook and scripts directories from the coverage report

Current behaviour

Currently, .storybook and scripts directories are included in the coverage report

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

• Tested in provided StackBlitz sandbox/Storybook
• Add new Playwright test coverage if required
• Carbon implementation matches Design System/designs
• UI Tests GitHub check reviewed if required

Additional context

Testing instructions

[carbonci]

🎉 This PR is included in version 158.28.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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