fix: PageHeader.ParentLink forwards rest props to support polymorphic as routing

[Copilot]

PageHeader.ParentLink destructured a fixed prop set and never spread the remainder onto the underlying Link, silently dropping any prop not in the allowlist — including to used by React Router. This broke the standard polymorphic pattern that works on Button, Link, and NavList.Item.

Changes

• PageHeader.tsx — Add ...rest to ParentLink's destructuring and spread it onto <Link> after the explicit props, matching the pattern used by other polymorphic Primer components
• PageHeader.test.tsx — Add two tests: one verifying arbitrary props (data-testid) reach the rendered element; one verifying a custom as component receives forwarded props (to)
• .changeset/pageheader-parentlink-rest-props.md — Patch changeset

// Now works as expected — `to` reaches the RouterLink
<PageHeader.ParentLink as={RouterLink} to="/somewhere">
  Back
</PageHeader.ParentLink>

Changelog

New

• None

Changed

• PageHeader.ParentLink now forwards unknown/rest props to the underlying element, consistent with other polymorphic Primer components

Removed

• None

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

Two new unit tests cover the fix:

1. data-testid forwarded via default as="a"
2. Custom as component (simulating a router Link) receives to and renders the correct href

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-ui (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 3ad321c

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

⚠️ Action required

👋 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. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[Copilot]

Pull request overview

Fixes PageHeader.ParentLink prop forwarding so it behaves consistently with other polymorphic Primer components (e.g. allowing React Router-style to when using a custom as component), instead of silently dropping unknown props.

Changes:

• Update PageHeader.ParentLink to collect ...rest props and spread them onto the underlying Link.
• Add unit tests verifying arbitrary props (e.g. data-testid) and custom as props (e.g. to) are forwarded correctly.
• Add a patch changeset for @primer/react.

Show a summary per file

File	Description
packages/react/src/PageHeader/PageHeader.tsx	Forwards remaining props from ParentLink onto Link, enabling polymorphic routing props like to.
packages/react/src/PageHeader/PageHeader.test.tsx	Adds regression tests ensuring rest props and custom as props are forwarded to the rendered link.
.changeset/pageheader-parentlink-rest-props.md	Declares a patch release note for the ParentLink prop-forwarding fix.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0

[primer-integration]

Integration test results from github/github-ui PR:

  CI Passed
  VRT Passed
  Projects Passed

All checks passed!