Failures on Extension types. Report when await of not Future subtype.

[whesse]

There are new test failures on Extension types. Report when await of not Future subtype..

The tests

co19/LanguageFeatures/Extension-types/static_analysis_extension_types_A08_t02 CompileTimeError (expected Pass)

are failing on configurations

analyzer-asserts-linux
analyzer-asserts-mac

If the test needs to be fixed, please file an issue on the co19 repo.

[eernstg]

The test has been fixed in https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Extension-types/static_analysis_extension_types_A08_t02.dart, fix should be effective after next roll.