[Feature][connector-jdbc][DB2] Optimize unit testing for DB2 in JDBC connector

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Description

This issue focuses on improving and expanding unit test coverage for the DB2 case in the connector-jdbc module, consistent with the scope defined in #10210.

1. At present, the unit tests of connector-jdbc code basically rely on the local environment and will be turned off during the actual running of ci, which will lead to functional risks. We hope to introduce docker containers and run unit tests in the actual ci process.
2. The unit test coverage of connector-jdbc code is relatively low, such as the jdbcCatalog test and jdbcDialect test. Additionally, there is a lack of boundary condition test cases. We hope to add relevant test cases.
3. After completing points 1 and 2, you can transfer the unit tests in the jdbc-e2e module to connector-jdbc.

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Are you willing to submit a PR?

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Code of Conduct

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