Update v3.0/how-to/maintain/identify-slow-queries.md
Update v3.0/how-to/maintain/identify-slow-queries.md

Co-Authored-By: Calvin Weng <03310b1688af3ac6d84b03af03b0c4d581e884d9@pingcap.com>
pingcap/docs-cn,pingcap/docs-cn