Stop calling close_all_sessions in forks (apache#47638)

This ends up not being safe, might be a race condition, but we
can get away with not doing it at all.

Co-authored-by: Ash Berlin-Taylor <[email protected]>

Author: jedcunningham

airflow/settings.py

@@ -388,11 +388,9 @@ def _session_maker(_engine):
     NonScopedSession = _session_maker(engine)
     Session = scoped_session(NonScopedSession)
 
-    from sqlalchemy.orm.session import close_all_sessions
-
-    os.register_at_fork(after_in_child=close_all_sessions)
     # https://docs.sqlalchemy.org/en/20/core/pooling.html#using-connection-pools-with-multiprocessing-or-os-fork
     os.register_at_fork(after_in_child=lambda: engine.dispose(close=False))
+    os.register_at_fork(after_in_child=lambda: async_engine.sync_engine.dispose(close=False))
 
 
 DEFAULT_ENGINE_ARGS = {