Update Duo Pro trial cta card copy

What does this MR do and why?

Update Duo Pro trial CTA card copy to be more accurate with current positioning of the Duo Pro offering

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

bin/rails c

Feature.enable(:duo_pro_trials)

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Sign in. Create new group.

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'ultimate'))

• Visit group's billing page. Make sure there is correct text in the card.

Related to #451290