Increased spacing between `River` components on mobile viewports

[joshfarrant]

List of notable changes:

• Increased River outer padding from var(--base-size-28) to var(--base-size-36) on mobile viewports

What should reviewers focus on?

Steps to test:

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

• Closes https://github.com/primer/brand/issues/783

Contributor checklist:

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

🦋 Changeset detected

Latest commit: 069dfae8f9cd8600e78dc399a6b0f3adb428fece

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

This PR includes changesets to release 6 packages

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

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[github-actions[bot]]

🔍 Design token changes found

View CSS variable changes

```diff - --brand-River-spacing-outer: var(--base-size-28); + --brand-River-spacing-outer: var(--base-size-36); ```

[github-actions[bot]]

⚠️ Visual differences found

Our visual comparison tests found UI differences.

Please review the differences by using the test artifacts to ensure that the changes were intentional. Artifacts can be downloaded and reviewed locally. Download links are available at the bottom of the workflow summary screen. ##### Example:  If the changes are expected, please run `npm run test:visual:update-snapshots` to replace the previous fixtures.

Review visual differences