chore: add missing slot checks

[francinelucca]

Found some components that were missing slots during testing

Changelog

New

• Add slot check and SLOT property to missing components that need it

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]

🦋 Changeset detected

Latest commit: 0349e9d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Patch
@primer/styled-react	Patch

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[Copilot]

Pull Request Overview

This PR adds missing slot checks to ensure components properly detect their child elements when used within Primer React's slot system. The slot system allows components to be wrapped while maintaining proper type detection for composition patterns.

• Adds isSlot checks alongside existing type checks for child element detection
• Adds __SLOT__ symbol properties to components that were missing them
• Updates TypeScript types to include FCWithSlotMarker where needed

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/react/src/internal/components/CheckboxOrRadioGroup/CheckboxOrRadioGroup.tsx	Adds slot checks for Label, Validation, and Caption child detection
packages/react/src/experimental/SelectPanel2/SelectPanel.tsx	Adds slot support for SelectPanelButton with type annotations and symbol
packages/react/src/TreeView/TreeView.tsx	Adds slot checks for SubTree component and updates type annotations
packages/react/src/SegmentedControl/SegmentedControl.tsx	Adds slot check for Button child detection in text extraction logic
packages/react/src/PageHeader/PageHeader.tsx	Adds slot checks for ContextArea and LeadingAction components with proper annotations
packages/react/src/ActionMenu/ActionMenu.tsx	Adds comprehensive slot checks for MenuButton and Anchor child detection

[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!

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/4481

[primer-integration]

🟢 ci completed with status success.