Adjust spacing in river breakout

[rezrah]

Summary

Closes #873
Part of https://github.com/github/primer/issues/4601

🔗 Storybook preview

List of notable changes:

• Reduced spacing between the main text and link in River Breakout component
• Applied a maximum width to the main text in River Breakout component
• Replaced Container with a wider Grid component decorator to be more representative of real-world usage

What should reviewers focus on?

• Review design changes are correct

Steps to test:

1. Storybook example
   

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
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• 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]

🦋 Changeset detected

Latest commit: 37ceba2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@primer/react-brand	Patch
@primer/brand-primitives	Patch
@primer/brand-e2e	Patch
@primer/brand-fonts	Patch
@primer/brand-config	Patch
@primer/brand-storybook	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

🔍 Design token changes found

View CSS variable changes

+ --brand-River-spacing-innerY: var(--base-size-24);

+ --brand-River-spacing-innerY: var(--base-size-24);

+ --brand-River-spacing-innerY: var(--base-size-32);

[rezrah]

@danielguillan @jesussandreas For breakout vertical spacing, i only have a reference point for desktop. Left mobile and tablets at 24px as before. Let me know if you feel it should also change.

[github-actions]

🟢 No visual differences found

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