Remove unused renderWithTheme helper from Breadcrumbs tests

[Copilot]

Addresses feedback on #7081 to remove the renderWithTheme helper function that no longer serves a purpose beyond wrapping HTMLRender.

Changes

• Removed renderWithTheme helper function definition
• Replaced all 15 usages with direct HTMLRender calls throughout test file

The helper was originally used to provide theming context but is now redundant after feature flag removal.

// Before
const renderWithTheme = (component: React.ReactElement) => HTMLRender(component)
renderWithTheme(<Breadcrumbs overflow="menu">...</Breadcrumbs>)

// After
HTMLRender(<Breadcrumbs overflow="menu">...</Breadcrumbs>)

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[changeset-bot]

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Latest commit: 9ce7af4

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!