Flaky test TestMysqlRouter

[lance6716]

https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftidb-tools%2Fpull_verify/detail/pull_verify/246/pipeline

--- FAIL: TestMysqlRouter (0.00s)

    source_test.go:540: 

        	Error Trace:	/home/jenkins/agent/workspace/pingcap/tidb-tools/pull_verify/tidb-tools/sync_diff_inspector/source/source_test.go:540

        	Error:      	Received unexpected error:

        	            	Query: could not match actual sql: "SELECT /*!40001 SQL_NO_CACHE */ `a`, `b`, round(`c`, 5-floor(log10(abs(`c`)))) as `c` FROM `source_test_t`.`test_t` WHERE ((((`a` > ?) OR (`a` = ? AND `b` > ?)) AND ((`a` < ?) OR (`a` = ? AND `b` <= ?))) AND ()) ORDER BY `a`,`b`" with expected regexp "SELECT COUNT.*"

        	            	github.com/pingcap/errors.AddStack

        	            		/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20240318064555-6bd07397691f/errors.go:178

        	            	github.com/pingcap/errors.Trace

        	            		/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20240318064555-6bd07397691f/juju_adaptor.go:15

        	            	github.com/pingcap/tidb-tools/sync_diff_inspector/source.(*MySQLSources).GetRowsIterator

        	            		/home/jenkins/agent/workspace/pingcap/tidb-tools/pull_verify/tidb-tools/sync_diff_inspector/source/mysql_shard.go:201

        	            	github.com/pingcap/tidb-tools/sync_diff_inspector/source.TestMysqlRouter

        	            		/home/jenkins/agent/workspace/pingcap/tidb-tools/pull_verify/tidb-tools/sync_diff_inspector/source/source_test.go:539

        	            	testing.tRunner

        	            		/usr/local/go/src/testing/testing.go:1690

        	            	runtime.goexit

        	            		/usr/local/go/src/runtime/asm_amd64.s:1700

        	Test:       	TestMysqlRouter