Implement MetaPathFinder.find_spec method in MyFinder subclass.

The `MyFinder` subclass of [`MetaPathFinder`](https://docs.python.org/3.11/library/importlib.html#importlib.abc.MetaPathFinder) currently only implements the deprecated `find_module` method. That deprecated method was [removed](python/cpython#98059) in Python 3.12. This change adds an implementation for its replacement method called `find_spec`.

python/helpers/generator3/core.py

@@ -592,6 +592,11 @@ def find_module(self, fullname, path=None):
             imported_names.add(fullname)
             return None
 
+        # noinspection PyMethodMayBeStatic
+        def find_spec(self, fullname, path, target=None):
+            imported_names.add(fullname)
+            return None
+
     my_finder = MyFinder()
     sys.meta_path.insert(0, my_finder)
     try: