Hosting dashboard: Fix sites thumbnail margin

[DustyReagan]

Related to #94202

Proposed Changes

• Removes extra margin on /sites thumbnails.

Before	After

Why are these changes being made?

• Improve aesthetics and readability.

Testing Instructions

• Use Calypso Live
• Go to /sites and ensure the site list and thumbnails look good in various widths.
• Try searching and filtering with different criteria to try and break the layout

Pre-merge Checklist

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

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-119202

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-119202&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-119202&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~31 bytes removed 📉 [gzipped])

name                parsed_size           gzip_size
staging-site             -109 B  (-0.0%)      -31 B  (-0.0%)
sites-dashboard          -109 B  (-0.0%)      -31 B  (-0.0%)
site-performance         -109 B  (-0.0%)      -31 B  (-0.0%)
site-monitoring          -109 B  (-0.0%)      -31 B  (-0.0%)
site-logs                -109 B  (-0.0%)      -31 B  (-0.0%)
hosting-features         -109 B  (-0.0%)      -31 B  (-0.0%)
hosting                  -109 B  (-0.0%)      -31 B  (-0.0%)
github-deployments       -109 B  (-0.0%)      -31 B  (-0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[allilevine]

Looks great! I tested at different screen widths and didn't see any issues. It looks like we originally added the margin as part of a thumbnail flickering fix, but I'm not seeing flickering without it.