Add tests for the indented syntax #1643

Job	Run time
JS API \| Pure JS \| Browser	1m 18s
JS API \| Pure JS \| Node lts/* \| ubuntu-latest	1m 20s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	4m 43s
JS API \| Pure JS \| Node lts/* \| windows-latest	3m 23s
Language \| Dart Sass \| Dart stable	1m 0s
JS API \| Embedded \| Node lts/* \| windows-latest	7m 19s
JS API \| Pure JS \| Node lts/* \| macos-latest	1m 50s
Language \| Dart Sass \| Dart dev	58s
Lint spec files	17s
JS API \| Embedded \| Node lts/* \| macos-latest	4m 4s
JS API \| Pure JS \| Node lts/-1 \| ubuntu-latest	1m 22s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	4m 56s
JS API \| Pure JS \| Node lts/-2 \| ubuntu-latest	1m 22s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	5m 7s
Unit tests	38s
JS API \| Pure JS \| Node lts/-3 \| ubuntu-latest	1m 24s
Static analysis	15s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	1m 39s
	42m 55s

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