Sites Dashboard: Layout improvements

[taipeicoder]

Related to p1729282075333529-slack-C048CUFRGFQ

Proposed Changes

This PR proposed some quick layout improvements to the sites dashboard.

Before:

After:

Not in scope:

• Optimizing alignment when scrollbar is always being shown.
• Making the table full-width for wide resolutions.

Why are these changes being made?

Contributes to the overall polish of WordPress.com

Testing Instructions

• Head to /sites
• Ensure that alignments are updated as shown above.
• Also test different resolutions and alignments still make sense.

Pre-merge Checklist

• [x] Has the general commit checklist been followed? (PCYsg-hS-p2)
• [x] Have you written new tests for your changes?
• [x] Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• [x] Have you checked for TypeScript, React or other console errors?
• [x] Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• [x] Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• [x] For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?