Undo the formatting fix

We ended up only bumping CI to Dart 3.0.0, and in 3.0.0 the old formatting is the correct one.

PiperOrigin-RevId: 571333640

Author: Ilya Yanok

lib/annotations.dart

@@ -149,10 +149,10 @@ class MockSpec<T> {
     Symbol? as,
     @Deprecated('Avoid adding concrete implementation to mock classes. '
         'Use a manual implementation of the class without `Mock`')
-    List<Type> mixingIn = const [],
+        List<Type> mixingIn = const [],
     @Deprecated('Specify "missing stub" behavior with the '
         '[onMissingStub] parameter.')
-    this.returnNullOnMissingStub = false,
+        this.returnNullOnMissingStub = false,
     this.unsupportedMembers = const {},
     this.fallbackGenerators = const {},
     this.onMissingStub,