Add hideDivider prop to NavList.Group

[TylerJDev]

Closes https://github.com/github/primer/issues/5407

Adds hideDivider prop to NavList.Group to allow consumers to toggle showing a divider when NavList.Group is rendered.

NavList.Group with divider	NavList.Group without divider (hideDivider prop)

Changelog

New

• Adds hideDivider prop to NavList.Group

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

[changeset-bot]

🦋 Changeset detected

Latest commit: eb3db75

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	Minor

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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. If this doesn't work, you can also use the original workflow here. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

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[Copilot]

Pull request overview

Adds an opt-out mechanism for the visual divider that precedes NavList.Group, matching the requested consumer control while preserving the existing default behavior.

Changes:

• Added a new optional hideDivider?: boolean prop to NavList.Group.
• Updated rendering so the leading ActionList.Divider is conditional on hideDivider.
• Added unit tests and documented the new prop; included a minor-release changeset.

Show a summary per file

File	Description
packages/react/src/NavList/NavList.tsx	Introduces hideDivider prop and conditionally renders the divider before a group.
packages/react/src/NavList/NavList.test.tsx	Adds tests verifying divider renders by default and is omitted when hideDivider is set.
packages/react/src/NavList/NavList.docs.json	Documents hideDivider in the generated docs metadata with default false.
.changeset/navlist-group-hide-divider.md	Declares a minor bump for the new NavList.Group prop.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Low

[joshblack]

@TylerJDev could you add a VRT test for this? I think it'd be helpful since it is a visual prop. Let me know what you think 👀