ToolsPanel: Sets column-gap to 16px for grid

[amitraj2203]

What?

Closes: #64488

Why?

To update the column gap from 8px to 16px according to the current specs

Screenshots or screencast

[github-actions]

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Co-authored-by: amitraj2203 <[email protected]>
Co-authored-by: mirka <[email protected]>

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[mirka]

Thanks! 🚀

[mirka]

Oh by the way, please add a changelog before merging 🙏

[github-actions]

Flaky tests detected in f9aa861.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/10404117736
📝 Reported issues:

• [Flaky Test] Redirection after template creation #60678 in /test/e2e/specs/site-editor/site-editor-url-navigation.spec.js