Fix invite a group on project wording and link

What does this MR do and why?

• fix wording and link for inviting a group from a project as per #393011
• fix margin bottom spacing under alert

Screenshots or screen recordings

source	before	after
project
group

How to set up and validate locally

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

bin/rails c

ApplicationSetting.first.update(dashboard_limit_enabled: true, dashboard_notification_limit: 3, dashboard_limit: 5, dashboard_enforcement_limit: 10)
Feature.enable(:free_user_cap)
Feature.enable(:free_user_cap_new_namespaces)
Feature.enable(:preview_free_user_cap)

• Sign in as admin or another user. Create private group and private project inside.
• Go to the group members page and click Invite a group.
• Validate notification.
• Go to the project members page and click Invite a group.
• Validate notification.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #393011