[hotfix][mysql][tests] Avoid canceling a finished job in tests of SpecificStartingOffsetITCase (#2687)

This closes #2687.

flink-cdc-connect/flink-cdc-source-connectors/flink-connector-mysql-cdc/src/test/java/com/ververica/cdc/connectors/mysql/source/SpecificStartingOffsetITCase.java

@@ -163,7 +163,6 @@ public class SpecificStartingOffsetITCase {
                                 savepointDir.toAbsolutePath().toString(),
                                 SavepointFormatType.DEFAULT)
                         .get();
-        jobClient.cancel().get();
 
         // Make some changes after the savepoint
         executeStatements(
@@ -239,7 +238,6 @@ public class SpecificStartingOffsetITCase {
                                 savepointDir.toAbsolutePath().toString(),
                                 SavepointFormatType.DEFAULT)
                         .get();
-        jobClient.cancel().get();
 
         // Make some changes after the savepoint
         executeStatements(
@@ -325,7 +323,6 @@ public class SpecificStartingOffsetITCase {
                                 savepointDir.toAbsolutePath().toString(),
                                 SavepointFormatType.DEFAULT)
                         .get();
-        jobClient.cancel().get();
 
         // Make some changes after the savepoint
         executeStatements(