Add tests for the indented syntax #1645

Job	Run time
JS API \| Pure JS \| Browser	1m 23s
Language \| Dart Sass \| Dart stable	1m 0s
Language \| Dart Sass \| Dart dev	1m 3s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	4m 44s
JS API \| Pure JS \| Node lts/* \| ubuntu-latest	1m 17s
Lint spec files	15s
JS API \| Embedded \| Node lts/* \| windows-latest	7m 28s
Static analysis	16s
JS API \| Pure JS \| Node lts/* \| windows-latest	3m 35s
JS API \| Embedded \| Node lts/* \| macos-latest	3m 44s
JS API \| Pure JS \| Node lts/* \| macos-latest	1m 13s
Unit tests	39s
JS API \| Pure JS \| Node lts/-1 \| ubuntu-latest	1m 23s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	4m 51s
JS API \| Pure JS \| Node lts/-2 \| ubuntu-latest	1m 19s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	5m 25s
JS API \| Pure JS \| Node lts/-3 \| ubuntu-latest	1m 24s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	1m 37s
	42m 36s

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