Test `@extend` without a selector #1675

Job	Run time
JS API \| Pure JS \| Browser	1m 21s
JS API \| Pure JS \| Node lts/* \| ubuntu-latest	1m 15s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	5m 1s
JS API \| Pure JS \| Node lts/* \| windows-latest	3m 36s
Language \| Dart Sass \| Dart stable	1m 1s
JS API \| Embedded \| Node lts/* \| windows-latest	7m 7s
JS API \| Pure JS \| Node lts/* \| macos-latest	1m 36s
Language \| Dart Sass \| Dart dev	59s
Lint spec files	15s
JS API \| Embedded \| Node lts/* \| macos-latest	4m 17s
JS API \| Pure JS \| Node lts/-1 \| ubuntu-latest	1m 22s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	4m 55s
JS API \| Pure JS \| Node lts/-2 \| ubuntu-latest	1m 18s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	5m 2s
JS API \| Pure JS \| Node lts/-3 \| ubuntu-latest	1m 21s
Unit tests	40s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	5m 32s
Static analysis	17s
	46m 55s

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