Trial PR to use an engine that has the null safety unfork CL in it. (#56309)

* Trial PR to use an engine that has the null safety unfork CL in it.

* Fix mack specification for test.

bin/internal/engine.version

-95ecd9a4050c38ce82a99c8fce70cacaf41a5a1b
+494a63c4117fec7ea4b3d8b01346522aa61cff68

packages/flutter_tools/test/general.shard/platform_plugins_test.dart

@@ -35,7 +35,7 @@ void main() {
 
       final MockFile pluginJavaMainClass = MockFile();
       when(pluginJavaMainClass.existsSync()).thenReturn(true);
-      when(pluginJavaMainClass.readAsStringSync()).thenThrow(const FileSystemException());
+      when(pluginJavaMainClass.readAsStringSync(encoding: anyNamed('encoding'))).thenThrow(const FileSystemException());
       when(mockFileSystem.file('.pub_cache/plugin_a/android/src/main/java/com/company/PluginA.java'))
         .thenReturn(pluginJavaMainClass);