Check for void in rules subtyping (fixes #25069)

pkg/analyzer/test/generated/type_system_test.dart

Index: pkg/analyzer/test/generated/type_system_test.dart
diff --git a/pkg/analyzer/test/generated/type_system_test.dart b/pkg/analyzer/test/generated/type_system_test.dart
index 4588d891d4c32443f7361f5df54a0d727ad4836e..e4501be0e6e27cb4dc6dddddce0792b8749b6af3 100644
--- a/pkg/analyzer/test/generated/type_system_test.dart
+++ b/pkg/analyzer/test/generated/type_system_test.dart
@@ -675,6 +675,13 @@ class StrongSubtypingTest {
         subtypes: subtypes);
   }
 
+  // Regression test for https://github.com/dart-lang/sdk/issues/25069
+  void test_isSubtypeOf_simple_function_void() {
+    FunctionType functionType =
+        TypeBuilder.functionType(<DartType>[intType], objectType);
+    _checkIsNotSubtypeOf(voidType, functionType);
+  }
+
   void test_isSubtypeOf_simple_function() {
     FunctionType top =
         TypeBuilder.functionType(<DartType>[intType], objectType);