Update FlashMigrationCounter guidance to reference un-deprecated component

[tomthorogood]

Authors: Please fill out this form carefully and completely.

Reviewers: By approving this Pull Request you are approving the code change, as well as its deployment and mitigation plans.
Please read this description carefully. If you feel there is anything unclear or missing, please ask for updates.

What are you trying to accomplish?

Fix guidance to use a non-deprecated component. Currently switching from a flash to Primer::Beta::Flash also fails with a recommendation to use Primer::Alpha::Banner instead.

Integration

No.

List the issues that this change affects.

#3693

Closes # (type the GitHub issue number after #)

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

What approach did you choose and why?

Anything you want to highlight for special attention from reviewers?

Accessibility

• Fixes axe scan violation - This change fixes an existing axe scan violation.
• No new axe scan violation - This change does not introduce any new axe scan violations.
• New axe violation - This change introduces a new axe scan violation. Please describe why the violation cannot be resolved below.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

Take a look at the What we look for in reviews section of the contributing guidelines for more information on how we review PRs.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 5fc9e67

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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

[Copilot]

Pull Request Overview

Updates the FlashMigrationCounter linter guidance to reference Primer::Alpha::Banner instead of the deprecated Primer::Beta::Flash component. This addresses an issue where the migration guidance was pointing to a deprecated component.

• Replaces references to Primer::Beta::Flash with Primer::Alpha::Banner in linter messages and component references
• Updates corresponding test expectations to reflect the new component guidance

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/primer/view_components/linters/flash_migration_counter.rb	Updates linter message and component constant to reference the non-deprecated Banner component
test/lib/erblint/flash_migration_counter_test.rb	Updates test assertion to expect the new Banner component in linter messages

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}