Add tests for the indented syntax #1640

Job	Run time
JS API \| Pure JS \| Browser	1m 25s
JS API \| Pure JS \| Node lts/* \| ubuntu-latest	1m 14s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	4m 54s
JS API \| Pure JS \| Node lts/* \| windows-latest	3m 26s
Lint spec files	17s
JS API \| Embedded \| Node lts/* \| windows-latest	7m 30s
Language \| Dart Sass \| Dart stable	1m 0s
JS API \| Pure JS \| Node lts/* \| macos-latest	1m 42s
JS API \| Embedded \| Node lts/* \| macos-latest	4m 7s
Language \| Dart Sass \| Dart dev	1m 7s
JS API \| Pure JS \| Node lts/-1 \| ubuntu-latest	1m 20s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	5m 21s
Static analysis	18s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	5m 13s
JS API \| Pure JS \| Node lts/-2 \| ubuntu-latest	1m 23s
JS API \| Pure JS \| Node lts/-3 \| ubuntu-latest	1m 27s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	1m 42s
Unit tests	39s
	44m 5s

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