fix(planner): add missing flink-table-code-splitter test dependency

[shoemoney]

What is the purpose of the change

Fix a test compilation failure in the planner module. JsonParseReuseTest.java imports org.apache.flink.table.codesplit.JavaCodeSplitter, but flink-table/flink-table-planner/pom.xml declares no test-scoped dependency on flink-table-code-splitter, so mvn -Dtest=CreateConnectionITCase fails to compile the test sources.

Brief change log

• Add a test-scoped dependency on flink-table-code-splitter to flink-table/flink-table-planner/pom.xml

Verifying this change

• Confirmed the import in JsonParseReuseTest.java fails to compile without the dependency
• Confirmed test compilation succeeds after adding it

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): yes, adds a test-scoped dependency on flink-table-code-splitter
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature?: no

[flinkbot]

CI report:

• 34067ce Azure: SUCCESS

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[uros-b]

Good fix, thank you @shoemoney!