Fix an analyzer warning in scheduled_test.

pkg/scheduled_test/test/utils.dart

Index: pkg/scheduled_test/test/utils.dart
diff --git a/pkg/scheduled_test/test/utils.dart b/pkg/scheduled_test/test/utils.dart
index e2b6fcd7921d899c98b679259282c587f251a60d..2d27b2df86e3fcd72155c1189524cc6f258f2269 100644
--- a/pkg/scheduled_test/test/utils.dart
+++ b/pkg/scheduled_test/test/utils.dart
@@ -62,7 +62,7 @@ void setUpTimeout() {
 /// Creates a metatest with [body] and asserts that it passes.
 ///
 /// This is like [expectTestsPass], but the [test] is set up automatically.
-void expectTestPasses(String description, void body()) =>
+void expectTestPasses(String description, Future body()) =>
   expectTestsPass(description, () => test('test', body));
 
 /// Creates a metatest that runs [testBody], captures its schedule errors, and
@@ -70,7 +70,7 @@ void expectTestPasses(String description, void body()) =>
 ///
 /// [testBody] is expected to produce an error, while [validator] is expected to
 /// produce none.
-void expectTestFails(String description, void testBody(),
+void expectTestFails(String description, Future testBody(),
     void validator(List<ScheduleError> errors)) {
   expectTestsPass(description, () {
     var errors;