logging: change event_name arg (#28232)

This doesn't change anything in practice, but makes it harder to write a bug where a kwarg with the name `event` would overwrite the event name.
old-commit-hash: 309126a527

common/logging_extra.py

@@ -153,9 +153,9 @@ class SwagLogger(logging.Logger):
   def bind_global(self, **kwargs):
     self.global_ctx.update(kwargs)
 
-  def event(self, event_name, *args, **kwargs):
+  def event(self, event, *args, **kwargs):
     evt = NiceOrderedDict()
-    evt['event'] = event_name
+    evt['event'] = event
     if args:
       evt['args'] = args
     evt.update(kwargs)