Fix nativeTest for Firebird optional module

[linghengqian]

For #35363 .

Changes proposed in this pull request:

• Fix nativeTest for Firebird optional module. Also see https://github.com/apache/shardingsphere/actions/runs/15045872527/job/42288136233 .
• In Remove unused dependencies in pom.xml #35363, Firebird became an optional module and therefore requires additional documentation.
• This PR further avoids using null actualDataNodes in the documentation, which is misleading.
• Executing org.apache.shardingsphere.test.natived.proxy.transactions.base.SeataTest unit test in Github Actions Runner may cause connection leaks in other unit tests. Pending investigation. However, this bug cannot be reproduced on local devices.

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