chore(Select): Remove the CSS modules feature flag from the Select component

[jonrohan]

Closes https://github.com/github/primer/issues/4299

Changelog

New

Changed

Removed

Remove the CSS modules feature flag from the Select component

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: 6bf8f70

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

Not sure what this means? Click here to learn what changesets are.

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

[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!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	98.68 KB (-0.06% 🔽)
packages/react/dist/browser.umd.js	98.91 KB (-0.07% 🔽)

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/376658

[primer-integration]

🟢 golden-jobs completed with status success.

[Copilot]

Pull Request Overview

Remove the CSS modules feature flag from the Select component and simplify its implementation.

• Drop all feature-flag toggles and styled-component variants in favor of a single native <select> with CSS modules.
• Update the ArrowIndicator to always use the CSS modules class.
• Remove legacy flag-based tests and adjust testing to the simplified API.

Reviewed Changes

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

File	Description
packages/react/src/tests/Select.test.tsx	Removed FeatureFlags import and legacy flag-based test cases
packages/react/src/Select/Select.tsx	Eliminated feature-flag logic and styled-component wrappers, simplified to native <select>
.changeset/loose-planes-mix.md	Added a changeset entry for removing the feature flag

Comments suppressed due to low confidence (1)

packages/react/src/tests/Select.test.tsx:21

• Add tests covering placeholder insertion and validationStatus behavior (e.g., verify that a placeholder option is rendered when placeholder is provided and that aria-invalid is set when validationStatus is 'error').

expect(render(<Element />).getAllByTestId('select-default')[0]).toHaveClass('test-class-name')

[Copilot]

The new <select> element no longer includes aria-invalid, data-hasplaceholder, or defaultValue props that were on the previous styled component; restoring these ensures accessible error reporting and correct placeholder behavior.