[fix](case) Fix test_backup_restore_atomic_with_alter with SYNC (apac…

…he#43601)

### What problem does this PR solve?

Execute SYNC command before executing any SELECT/SHOW commands, to avoid
staled read

regression-test/suites/backup_restore/test_backup_restore_atomic_with_alter.groovy

@@ -108,6 +108,7 @@ suite("test_backup_restore_atomic_with_alter", "backup_restore") {
             "atomic_restore" = "true"
         )
     """
+    sql "SYNC"
 
     boolean restore_paused = false
     for (int k = 0; k < 60; k++) {
@@ -121,6 +122,8 @@ suite("test_backup_restore_atomic_with_alter", "backup_restore") {
     }
     assertTrue(restore_paused)
 
+    sql "SYNC"
+
     // 0. table_1 has in_atomic_restore property
     def show_result = sql """ SHOW CREATE TABLE ${dbName}.${tableNamePrefix}_1 """
     logger.info("SHOW CREATE TABLE ${tableNamePrefix}_1: ${show_result}")
@@ -224,6 +227,7 @@ suite("test_backup_restore_atomic_with_alter", "backup_restore") {
 
 
     sql "CANCEL RESTORE FROM ${dbName}"
+    sql "SYNC"
 
     // 5. The restore job is cancelled, the in_atomic_restore property has been removed.
     show_result = sql """ SHOW CREATE TABLE ${dbName}.${tableNamePrefix}_1 """