Update SelectPanel2 tests from Jest to Vitest

[joshblack]

Batch: https://github.com/github/primer/issues/5336

This issue tracks updating the SelectPanel2 tests from Jest to Vitest. If you want to use Copilot for this, you can use the prompt below with either Agent mode locally or by assigning copilot to this issue directly.

Copilot instructions

We are moving our test suite from Jest to Vitest. We've migrated some test files already, you can use packages/react/src/Banner/Banner.test.tsx as an example. When migrating, make sure to:

• Update packages/react/src/vitest.config.browser.mts to include the component that you're migrating in the include config
• Update packages/react/src/jest.config.js to exclude the component that you're migrating in the modulePathIgnorePatterns config
• Remove any behavesAsComponent usage
• Remove any checkExports usage
• Remove any tests that make axe assertions with toHaveNoViolations
• Remove any setupMatchMedia usage
• Update tests that use render from utils/testing to instead use render from @testing-library/react
• Use npx vitest --run with the path to the test file you've updated to validate your changes
• You can update snapshots using npx vitest --run -u with the path to the test file you would like to update snapshots for
• Do not migrate test files that are for types, these files end with *.types.test.tsx
• If you run into a test that uses it.skip, you can enable it now that we're moving to vitest

After migrating all components:

• Use npx prettier --write with the path to the test files to format the file according to the prettier rules on the project
• Use npx eslint with the path to the test files you've updated to make sure there are no eslint errors with your changes

Make sure to keep in mind:

• All npx commands should be run from the root of the project
• Tests should not emit an act() warning when updated
• Do not remove any tests when migrating