For #28968, fix query for proxy_frontend_database_protocol_type #7673

Job	Run time
Import Global Environment / init-environment	2s
E2E - Agent with MySQL (proxy, tracing, jaeger)	9m 23s
E2E - Agent with MySQL (proxy, tracing, zipkin)	5m 53s
E2E - Agent with MySQL (proxy, metrics, prometheus)	6m 0s
E2E - Agent with MySQL (proxy, logging, file)	8m 58s
E2E - Agent with MySQL (jdbc, logging, file)	8m 0s
E2E - Agent with MySQL (jdbc, metrics, prometheus)	9m 19s
E2E - Agent with MySQL (jdbc, tracing, jaeger)	9m 3s
E2E - Agent with MySQL (jdbc, tracing, zipkin)	7m 47s
	1h 4m 25s

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