chore(PPDSC-2675): speed up unit tests local run

[Xin00163]

PPDSC-2675

What I have done:

• Fix the disabled state in svg-previewer.tsx
• Update svg-previewer.test.tsx
• Update outdated docsite unit tests
• Increase local run maxWorker to 50% (this command is optional as not everyone wants to use 50%)

But if it's enabled, there is a dramatic difference:

Before:

After:

I have done:

• Written unit tests against changes
• Written functional tests against the component and/or NewsKit site
• Updated relevant documentation

I have tested manually:

• The feature's functionality is working as expected on Chrome, Firefox, Safari and Edge
• The screen reader reads and flows through the elements as expected.
• There are no new errors in the browser console coming from this PR.
• When visual test is not added, it renders correctly on different browsers and mobile viewports (Safari, Firefox, small mobile viewport, tablet)
• The Playground feature is working as expected

Before:

After:

Who should review this PR:

How to test:

[pp-serviceaccount]

You can preview these changes on:
Documentation Site: http://ncu-newskit-docs.s3-website-eu-west-1.amazonaws.com/ppdsc-2675-unit-tests-slow
Storybook: http://ncu-newskit-docs.s3-website-eu-west-1.amazonaws.com/ppdsc-2675-unit-tests-slow/storybook

[JohnTParsons]

Good work. I don't think you should be changing yarn.lock though as package.json has not changed

[Xin00163]

Good work. I don't think you should be changing yarn.lock though as package.json has not changed

I ran yarn upgrade interactive to upgrade the testing library package, which clearly was not needed. Now I need to revert it back