Add achievement icon padding

What does this MR do and why?

Add some padding in the user achievement icon.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

• Run the achievements seed script: bundle exec rake db:seed_fu FILTER=36_achievements
• Enable the feature flag in the rails console: Feature.enable(:achievements)
• Visit http://gdk.test:3000/root

If you have any problems, try deleting all achievements from the rails console: Achievements::Achievement.delete_all then re-running the seed script (not from the rails console): bundle exec rake db:seed_fu FILTER=36_achievements 🤞

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.