Performance Profiler: updates calypso loader bg color.

[cpapazoglou]

Fixes https://github.com/Automattic/dotcom-forge/issues/8859

Proposed Changes

• Adds a background pattern similar to other /speed-test pages

Testing Instructions

• Load http://calypso.localhost:3000/speed-test-tool?url=https%3A%2F%2Fwww.mathema.me%2F&hash=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6Njk3Nn0.Jn_1t7YcV-YzB7L10e4Zr9_2cqt44MyqPq6Lhw22zDU&tab=mobile
• Check that the Calypso loader with the W logo has a background similar to the page loaded.

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-119359

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-119359&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-119359&env=a8c-for-agencies

[cpapazoglou]

Added :not(.is-focus-content) to avoid the bg leaking to other cases.

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/performance-profiler-calypso-bg-color on your sandbox.