chore: add scss unit tests #5360

Job	Run time
Status check > Unit	1s
CI \| Unit	1s
CI \| Visual	1s
Compile themes / run	1m 1s
Lint scripts / run	32s
Lint styles / run (default)	1m 18s
Render test pages / verify	7s
Lint styles / run (bootstrap)	1m 27s
Lint styles / run (material)	1m 20s
Lint styles / run (classic)	1m 22s
Lint styles / run (fluent)	1m 19s
Render test pages / run	0s
Status check > Lint scripts	0s
Status check > A11y / prepare	1s
Create screenshots / run (default)	2m 9s
Create screenshots / run (bootstrap)	2m 27s
Create screenshots / run (material)	2m 37s
Create screenshots / run (classic)	2m 23s
Create screenshots / run (fluent)	2m 36s
Status check > A11y / run-checks (1)	2m 23s
Status check > A11y / run-checks (2)	2m 21s
Status check > A11y / run-checks (3)	2m 26s
Status check > A11y / run-checks (4)	2m 34s
Status check > Lint styles	1s
Detect changes	14s
Status check > Visual	1s
	30m 42s

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