util: fix data race in stmtSummaryByDigestMap (#31683)
util: fix data race in stmtSummaryByDigestMap (#31683)

close pingcap/tidb#31642
c4pt0r/tidb,c4pt0r/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,ngaut/tidb,pingcap/tidb,ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb