Resolve handler close race condition at triggerer shutdown (#37206)

At shutdown, a trigger may emit a "close" signal around the same time as logging.shutDown is called, so the handler may have been removed from the handlers by one thread when the other tries to delete it.

(cherry picked from commit e24f0a9)

airflow/utils/log/trigger_handler.py

@@ -19,6 +19,7 @@
 
 import asyncio
 import logging
+from contextlib import suppress
 from contextvars import ContextVar
 from copy import copy
 from logging.handlers import QueueHandler
@@ -110,17 +111,16 @@ def close_one(self, trigger_id):
         h = self.handlers.get(trigger_id)
         if h:
             h.close()
-            del self.handlers[trigger_id]
+            with suppress(KeyError):  # race condition between `handle` and `close`
+                del self.handlers[trigger_id]
 
     def flush(self):
         for h in self.handlers.values():
             h.flush()
 
     def close(self):
         for trigger_id in list(self.handlers.keys()):
-            h = self.handlers[trigger_id]
-            h.close()
-            del self.handlers[trigger_id]
+            self.close_one(trigger_id)
 
 
 class LocalQueueHandler(QueueHandler):