Add relative color syntax tests for the color() function #1507

Job	Run time
Unit tests	38s
Lint spec files	18s
Language \| Dart Sass \| Dart stable	1m 14s
JS API \| Pure JS \| Browser	1m 18s
Language \| Dart Sass \| Dart dev	1m 10s
Static analysis	21s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	4m 40s
JS API \| Embedded \| Node lts/* \| windows-latest	6m 56s
JS API \| Embedded \| Node lts/* \| macos-latest	3m 39s
JS API \| Pure JS \| Node lts/* \| ubuntu-latest	1m 16s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	4m 49s
JS API \| Pure JS \| Node lts/* \| windows-latest	3m 34s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	4m 51s
JS API \| Pure JS \| Node lts/* \| macos-latest	1m 12s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	1m 40s
JS API \| Pure JS \| Node lts/-1 \| ubuntu-latest	1m 22s
JS API \| Pure JS \| Node lts/-2 \| ubuntu-latest	1m 16s
JS API \| Pure JS \| Node lts/-3 \| ubuntu-latest	1m 29s
	41m 43s

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