Add Pull Request checks list story to Spinner examples

[Copilot]

Closes #

Adds an interactive Storybook example demonstrating Spinner in a GitHub PR checks UI pattern. Shows pending checks with spinners that transition to success/failure icons.

Changes

New story: PullRequestChecks

• Displays list of 4 simulated checks (Build, Lint, Type Check, Tests)
• Spinners for pending state, CheckCircleFillIcon for success, XCircleFillIcon for failure
• Interactive "Run checks" button simulates sequential check execution
• Uses Stack for layout, Text for typography, design tokens for styling
• Includes screen reader announcements on completion

Screenshots

Initial state with pending checks:

Completed checks:

Changelog

New

• PullRequestChecks story in Spinner.examples.stories.tsx
• CSS classes for checks list layout: .ChecksList, .CheckItem, .CheckIcon, .CheckContent, .CheckDescription

Changed

None

Removed

None

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; Storybook example only, no API changes

Testing & Reviewing

Story available at: Components → Spinner → Examples → Pull Request Checks

Click "Run checks" to see spinner → icon transitions

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

Original prompt

Add a story in Spinner.examples.stories.tsx that is a list of pull request checks based on github's ui.

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[changeset-bot]

⚠️ No Changeset found

Latest commit: f8629a6

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.