[CTABanner] Fix container width

[josepmartins]

Summary

Adjust width property to avoid shrinking when using Stack or Grid components as wrappers.

List of notable changes:

• added width: 100% to .CTABanner

What should reviewers focus on?

• Using Stack or Grid components on a CTABanner works as expected and doesn't shrink the wrapper

Steps to test:

1. Open the CTABanner component in storybook
2. Add display:flex to the parent
3. Verify that CTABanner behaves as described in the following issue.

Supporting resources (related issues, external links, etc):

• Slack thread: https://github.slack.com/archives/C04E44ZPNEA/p1683546014522099

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• New visual snapshots have been generated / updated for any UI changes
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

Screenshots:

Please try to provide before and after screenshots or videos

Before	After

[changeset-bot]

⚠️ No Changeset found

Latest commit: f7e9b21

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[github-actions]

🟢 No design token changes found

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.