chore: add IssueLabelToken Custom Colors VRT

[francinelucca]

Adds VRT for IssueLabelToken custom colors story

Changelog

New

• VRT for IssueLabelToken with Custom Colors story

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

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)

[changeset-bot]

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Latest commit: cc92103

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Pull Request Overview

Adds visual regression test coverage for the new IssueLabelToken custom color variants by including its Storybook story in the Token e2e test matrix.

• Extends the stories array with the custom colors scenario
• Prepares VRT to validate rendering of custom color configurations