fix(checkbox): update box color to neutral in s2

[TarunAdobe]

Description

Update deselected border color of checkbox to neutral.
SWC-498

How and where has this been tested?

Please tag yourself on the tests you've marked complete to confirm the tests have been run by someone other than the author.

Validation steps

Regression testing

Validate:

1. The documentation pages for at least two other components are still loading, including:

• The pages render correctly, are accessible, and are responsive.

2. If components have been modified, VRTs have been run on this branch:

• VRTs have been run and looked at.
• Any VRT changes have been accepted (by reviewer and/or PR author), or there are no changes.

Screenshots

To-do list

• I have read the contribution guidelines.
• I have updated relevant storybook stories and templates.
• I have tested these changes in Windows High Contrast mode.
• If my change impacts other components, I have tested to make sure they don't break.
• If my change impacts documentation, I have updated the documentation accordingly.
• ✨ This pull request is ready to merge. ✨

[changeset-bot]

🦋 Changeset detected

Latest commit: 0665550

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

This PR includes changesets to release 1 package

Name	Type
@spectrum-css/checkbox	Patch

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[github-actions]

File metrics

Summary

Total size: 2.25 MB^*

Package	Size	Minified	Gzipped
checkbox	22.43 KB	21.35 KB	2.56 KB

checkbox

Filename	Head	Minified	Gzipped	Compared to base
index-base.css	22.03 KB	20.97 KB	2.52 KB	-
index-theme.css	1.14 KB	1.12 KB	0.51 KB	-
index.css	22.43 KB	21.35 KB	2.56 KB	🔴 ⬆ 0.02 KB
metadata.json	12.69 KB	-	-	🟢 ⬇ 0.03 KB
themes/express.css	1.04 KB	1.01 KB	0.51 KB	-
themes/spectrum-two.css	1.01 KB	1.01 KB	0.52 KB	🔴 ⬆ 0.02 KB
themes/spectrum.css	1.04 KB	1.01 KB	0.52 KB	-

* Size is the sum of all main files for packages in the library.
* An ASCII character in UTF-8 is 8 bits or 1 byte.

[github-actions]

🚀 Deployed on https://pr-3573--spectrum-css.netlify.app

[castastrophe]

@TarunAdobe Can you please update the branch with the base branch and write out a few validation test cases in the pull request template for us to confirm the updates?