Update mixed-decl tests to reflect the improved implementation #1571

Job	Run time
Unit tests	41s
Lint spec files	18s
Static analysis	19s
Language \| Dart Sass \| Dart ${{ matrix.dart_channel }}	0s
JS API \| Pure JS \| Node ${{ matrix.node_version }} \| ${{ matrix.os }}	0s
JS API \| Pure JS \| Browser	0s
JS API \| Embedded \| Node lts/* \| ubuntu-latest	4m 43s
JS API \| Embedded \| Node lts/* \| windows-latest	7m 17s
JS API \| Embedded \| Node lts/* \| macos-latest	3m 32s
JS API \| Embedded \| Node lts/-1 \| ubuntu-latest	5m 0s
JS API \| Embedded \| Node lts/-2 \| ubuntu-latest	5m 6s
JS API \| Embedded \| Node lts/-3 \| ubuntu-latest	1m 38s
	28m 34s

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