[hotfix][oceanbase] Fix CI test failures: set OB_MEMORY_LIMIT and fix connector identifier

1. Set OB_MEMORY_LIMIT=4G for OceanBase test container. The default
   6G exceeds available memory in GitHub Actions runners when OceanBase
   tests run after other connector tests.

2. Fix OceanBaseFailoverITCase using 'mysql-cdc' instead of
   'oceanbase-cdc' as the connector identifier, which caused failover
   tests to exercise the wrong connector factory.

Author: yuanoOo

flink-cdc-connect/flink-cdc-source-connectors/flink-connector-oceanbase-cdc/src/test/java/org/apache/flink/cdc/connectors/oceanbase/OceanBaseFailoverITCase.java

@@ -344,7 +344,7 @@ private void testMySqlParallelSource(
                                         ? ""
                                         : ", primary key (id) not enforced")
                                 + ") WITH ("
-                                + " 'connector' = 'mysql-cdc',"
+                                + " 'connector' = 'oceanbase-cdc',"
                                 + " 'scan.incremental.snapshot.enabled' = 'true',"
                                 + " 'hostname' = '%s',"
                                 + " 'port' = '%s',"

flink-cdc-connect/flink-cdc-source-connectors/flink-connector-oceanbase-cdc/src/test/java/org/apache/flink/cdc/connectors/oceanbase/OceanBaseTestUtils.java

@@ -45,6 +45,7 @@ public static OceanBaseContainer createOceanBaseContainer(String version, String
         return new OceanBaseContainer(version)
                 .withMode(mode)
                 .withTenantPassword(TEST_PASSWORD)
+                .withEnv("OB_MEMORY_LIMIT", "4G")
                 .withEnv("OB_DATAFILE_SIZE", "2G")
                 .withEnv("OB_LOG_DISK_SIZE", "4G")
                 .withLogConsumer(new Slf4jLogConsumer(LOG));