update for python 3.12

cf https://searchfox.org/mozilla-esr102/source/third_party/python/virtualenv/virtualenv/run/plugin/base.py
Index: third_party/python/virtualenv/virtualenv/run/plugin/base.py
--- third_party/python/virtualenv/virtualenv/run/plugin/base.py.orig
+++ third_party/python/virtualenv/virtualenv/run/plugin/base.py
@@ -15,7 +15,7 @@ class PluginLoader(object):
 
     @classmethod
     def entry_points_for(cls, key):
-        return OrderedDict((e.name, e.load()) for e in cls.entry_points().get(key, {}))
+        return OrderedDict((e.name, e.load()) for e in cls.entry_points().select(group=key))
 
     @staticmethod
     def entry_points():
