anchor.diff:  
   Map<String, dynamic> _selfValidateTaskConfig() => _githubJobYaml(
         selfValidateJobName,
  -      'ubuntu-latest',
  +      _ubuntuLatest,
         PackageFlavor.dart,
         'stable',
         [
  
positive.code:   String get _githubJobOs {
      switch (job.os) {
        case 'linux':
          return 'ubuntu-latest';
        case 'windows':
          return 'windows-latest';
        case 'osx':
  
negative.code:       ],
      );
  
  const _ubuntuLatest = 'ubuntu-latest';
  
  /// Used as a place-holder so we can treat all jobs the same in certain
  /// workflows.
  class _SelfValidateJob implements HasStageName {
  