#7643568 Update sale banner copy

Proposed Changes

Update sale banner copy to communicate that the sale is only for new purchases

Testing Instructions

1. Start your local environment via yarn start-jetpack-cloud
2. Go to http://jetpack.cloud.localhost:3000/pricing
3. Confirm sale banner copy is updated correctly
   

Context: p1669665511987229-slack-C02L8G7V18X

Pre-merge Checklist

• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?