Potentially unintended runtime error in a pattern test

[chloestefantsova]

The following lines in the test result in a runtime error.

co19/LanguageFeatures/Patterns/scope_A02_t04.dart

Lines 26 to 30 in 8db40c0

	const c = [[3], [4]];
	main() {
	var l = [1, 2, for (var [c] in [c]) c, 5];
	Expect.listEquals([1, 2, 3, 4, 5], l);

The constant list c that contains two elements is destructed as [c], that is, as a list of one element. That leads to the runtime error.