fix(Listbox): improve typing for ListBox

[Bracciata]

Summary

Closes #1890

• Replaces the generic PolymorphicComponent cast with a custom ListboxComponent overloaded type that properly discriminates between single-select and multi-select variants
• Fixes TypeScript error when using <Listbox> without explicitly passing multiselect (single-select is now the default)
• Updates @ts-expect-error comment in ActionList to reflect the actual type conflict (HTML attribute defaultValue vs ListboxValue)
• Adds compile-time type tests to verify single-select, multi-select, and invalid usage are all typed correctly

Test plan

• tsc passes without errors for single-select <Listbox value="foo"> (no multiselect prop)
• tsc catches invalid usage (e.g. multiselect with a string value)
• Existing Listbox unit tests still pass

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[Copilot]

Pull request overview

This PR fixes TypeScript typing/discrimination for the React Listbox component so single-select usage works without explicitly providing multiselect, while preserving correct multi-select typing and adding compile-time type coverage.

Changes:

• Introduces an overloaded ListboxComponent type to discriminate single-select vs multi-select props.
• Adds TypeScript “type test” JSX usages in Listbox tests to validate valid/invalid prop combinations at compile time.
• Updates the @ts-expect-error explanation in ActionList to reflect the actual conflicting prop types.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
packages/react/src/components/Listbox/Listbox.tsx	Replaces the broad polymorphic cast with an overloaded component type for correct single vs multi select prop discrimination.
packages/react/src/components/Listbox/index.test.tsx	Adds compile-time type-check examples to ensure the Listbox overloads behave as intended.
packages/react/src/components/ActionList/ActionList.tsx	Updates the @ts-expect-error comment to describe the real type conflict when spreading HTML attrs into Listbox.

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