Fix sensor loop handle cleanup

Summary:
TIL that pop_stack doesn't actually close the contextmanagers in the stack! https://docs.python.org/3/library/contextlib.html#contextlib.ExitStack.pop_all

I think what we actually want is close().

Resolves #3757.

Test Plan: Run daemon loop long enough that the pop_all is hit (>60 seconds), CTRL-C the daemon, daemon no longer hangs.

Reviewers: prha, johann, alangenfeld

Reviewed By: johann

Differential Revision: https://dagster.phacility.com/D6757

python_modules/dagster/dagster/scheduler/sensor.py

@@ -144,7 +144,7 @@ def execute_sensor_iteration_loop(
                 not handle_manager
                 or (start_time - manager_loaded_time) > RELOAD_LOCATION_MANAGER_INTERVAL
             ):
-                stack.pop_all()  # remove the previous context
+                stack.close()  # remove the previous context
                 handle_manager = stack.enter_context(
                     RepositoryLocationHandleManager(grpc_server_registry)
                 )