fix: playground button opens a new tab

[gui-santos]

Purpose of PR

Makes the button an anchor tag so it's possible to open the playground in a new tab

PR Checklist

• I have read the relevant readme.md file(s)
• All commits follow our Git commit message convention
• Tests are added/updated/not required
• Tests are passing
• Storybook stories are added/updated/not required
• Usage notes are added/updated/not required
• Has been tested based on Contentful's browser support
• Doesn't contain any sensitive information

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/contentful-apps/forma-36/3gJA36wbX9xtfbamrd8uRXeYXUsZ
✅ Preview: https://forma-36-git-fix-open-playground-button-contentful-apps.vercel.app

[changeset-bot]

⚠️ No Changeset found

Latest commit: cd57ad1

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.

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