Ignore built Godot.app package

Following the "compiling for mac" tutorial one will eventually end with a Godot.app package inside the repo folder. To prevent it from being tracked by git, it has been added to gitignore.

.gitignore

@@ -363,6 +363,7 @@ cpp.hint
 # macOS
 .DS_Store
 __MACOSX
+Godot.app
 
 # Windows
 # https://github.com/github/gitignore/blob/main/Global/Windows.gitignore