Add tests for the indented syntax #1642

Job	Run time
Lint spec files	15s
Static analysis	19s
Language \| Dart Sass \| Dart stable	1m 6s
JS API \| Pure JS \| Node lts/* \| ubuntu-latest	1m 17s
Language \| Dart Sass \| Dart dev	1m 0s
Unit tests	41s
JS API \| Pure JS \| Node lts/* \| windows-latest	2m 49s
JS API \| Pure JS \| Node lts/* \| macos-latest	1m 20s
JS API \| Pure JS \| Browser	1m 34s
JS API \| Pure JS \| Node lts/-1 \| ubuntu-latest	1m 20s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	4m 53s
JS API \| Pure JS \| Node lts/-2 \| ubuntu-latest	1m 16s
JS API \| Embedded \| Node lts/* \| windows-latest	6m 10s
JS API \| Pure JS \| Node lts/-3 \| ubuntu-latest	1m 25s
JS API \| Embedded \| Node lts/* \| macos-latest	4m 49s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	5m 1s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	5m 7s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	1m 40s
	42m 2s

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