Add tests for keeping interpolation in CSS custom properties declarat… #162

Job	Run time
Dart tests \| Dart stable \| ubuntu-latest	1m 10s
Dart tests \| Dart stable \| windows-latest	1m 39s
Static analysis	23s
Dart tests \| Dart stable \| macos-latest	1m 58s
Node tests \| Dart stable \| Node 18 \| ubuntu-latest	1m 5s
Node tests \| Dart stable \| Node 18 \| windows-latest	2m 53s
Node tests \| Dart stable \| Node 18 \| macos-latest	1m 50s
Node tests \| Dart stable \| Node 16 \| ubuntu-latest	1m 1s
Node tests \| Dart stable \| Node 14 \| ubuntu-latest	1m 8s
Node tests \| Dart dev \| Node \| ubuntu-latest	59s
Sanity checks	0s
Deploy Pub	0s
Deploy Homebrew	0s
Deploy Github: Linux	0s
Deploy npm	0s
Deploy Github: Mac OS	0s
Deploy Github: Windows	0s
	14m 6s

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