Update celery beat entrypoint for celery 5

The docs are here https://docs.celeryq.dev/en/stable/reference/celery.apps.beat.html
This was breaking in production as we were using an outdated call to the celery beat binary. Help from this stack overflow comment: https://stackoverflow.com/a/65213590

banzai/main.py

@@ -174,10 +174,8 @@ def start_stacking_scheduler():
                               schedule_calibration_stacking.s(site=site, runtime_context=vars(runtime_context)),
                               queue=runtime_context.CELERY_TASK_QUEUE_NAME)
 
-    beat = celery.bin.beat.beat(app=app)
+    app.Beat(schedule='/tmp/celerybeat-schedule', pidfile='/tmp/celerybeat.pid', working_directory='/tmp').run()
     logger.info('Starting celery beat')
-    beat.run(schedule='/tmp/celerybeat-schedule', pidfile='/tmp/celerybeat.pid', working_directory='/tmp')
-
 
 def run_realtime_pipeline():
     extra_console_arguments = [{'args': ['--n-processes'],