fix(move-tables): address Copilot review comments on #1704 (#8209)

- Add mgtr.checkAbort() at top of T3 drain poll loop so abort/panic
  stops the drain immediately instead of waiting the full 60s timeout
- Assert NoError on CREATE DATABASE IF NOT EXISTS in applier_test.go
  SetupSuite (was silently discarding the error with _, _ =)
- Rewrite T2 comment to frame @@GLOBAL.gtid_executed as a readability
  divergence (making scope unambiguous in SQL) rather than asserting
  session-vs-global semantics that may not hold in MySQL 8.0

Ref: database-infrastructure#8209

Author: womoruyi

go/logic/applier_test.go

@@ -301,7 +301,8 @@ func (suite *ApplierTestSuite) SetupSuite() {
 	suite.Require().NoError(err)
 
 	// Second database & connection for move-tables tests:
-	_, _ = suite.db.ExecContext(ctx, fmt.Sprintf("CREATE DATABASE IF NOT EXISTS %s", testMysqlDatabaseOther))
+	_, err = suite.db.ExecContext(ctx, fmt.Sprintf("CREATE DATABASE IF NOT EXISTS %s", testMysqlDatabaseOther))
+	suite.Require().NoError(err)
 	otherConf := drivermysql.NewConfig()
 	otherConf.DBName = testMysqlDatabaseOther
 	otherConf.User = testMysqlUser

go/logic/migrator.go

@@ -989,9 +989,9 @@ func (mgtr *Migrator) moveTablesCutOver() (err error) {
 	}
 
 	// ----- T2: capture @@gtid_executed on the SAME *sql.DB handle as T1 -----
-	// Design doc specifies @@gtid_executed; using @@global.gtid_executed because
-	// the unqualified form resolves to session scope (only this session's GTIDs),
-	// while drain requires the global GTID set (all committed transactions).
+	// The design doc specifies @@gtid_executed. We query @@GLOBAL.gtid_executed explicitly rather than the unqualified
+	// @@gtid_executed form to make the global server-wide scope unambiguous
+	// in the SQL itself.
 	// Design: https://github.com/github/gh-ost-tablemove-poc/blob/9dc6df75c4c88ff473906a497836c7518f5614ec/design/coop_cutover.md#32-correctness-verification-for-p4
 	var drainGTIDStr string
 	if err := mgtr.inspector.db.QueryRow("select @@global.gtid_executed").Scan(&drainGTIDStr); err != nil {
@@ -1022,6 +1022,9 @@ func (mgtr *Migrator) moveTablesCutOver() (err error) {
 	ticker := time.NewTicker(moveTablesCutOverDrainPollInterval)
 	defer ticker.Stop()
 	for {
+		if err := mgtr.checkAbort(); err != nil {
+			return err
+		}
 		mgtr.applier.CurrentCoordinatesMutex.Lock()
 		applierCoords := mgtr.applier.CurrentCoordinates
 		mgtr.applier.CurrentCoordinatesMutex.Unlock()