Skip CSS re-scoping in package-manager.spec

[Rheeseyb]

Problem:
We introduced @scope scoping into imported CSS in #4613, but this is causing issues with jsdom when running package-manager.spec, often causing a Heap Out Of Memory error when running on CI, leading to the jest job timing out.

Fix:
Since we aren't even testing the @scope scoping in the affected tests, I've used a mock to skip it. We have other tests in css-utils.spec for ensuring the scoping is working correctly.

[github-actions]

Try me

[relativeci]

Job #9938: Bundle Size — 62.22MiB (~-0.01%).

0703b38(current) vs 8f5e3ac master#9937(baseline)

Warning

Bundle contains 66 duplicate packages – View duplicate packages

Bundle metrics   2 changes 1 improvement

	Current Job #9938	Baseline Job #9937
Initial JS	45.41MiB(~-0.01%)	45.41MiB
Initial CSS	0B	0B
Cache Invalidation	19.85%	21.67%
Chunks	26	26
Assets	30	30
Modules	4368	4368
Duplicate Modules	471	471
Duplicate Code	30.72%	30.72%
Packages	462	462
Duplicate Packages	65	65

Bundle size by type   1 change 1 improvement

	Current Job #9938	Baseline Job #9937
JS	62.21MiB (~-0.01%)	62.21MiB
HTML	11.54KiB	11.54KiB

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View job #9938 report View fix/package-manager-css-tests branch activity View project dashboard

[github-actions]

Performance test results: