Add tests for Hive plugin registration

[zhangxinyao88]

Add focused coverage for HivePlugin to verify that it keeps the expected plugin name and registers the Hive macros.

Remove the corresponding entry from OVERLOOKED_TESTS now that the test module exists.

related: #35442

Testing:

• breeze run pytest providers/apache/hive/tests/unit/apache/hive/plugins/test_hive.py -xvs
• breeze run pytest airflow-core/tests/unit/always/test_project_structure.py::TestProjectStructure::test_providers_modules_should_have_tests -xvs
• Airflow pre-commit and commit-message hooks

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Was generative AI tooling used to co-author this PR?

• Yes (Codex)

Generated-by: Codex following the guidelines

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Drafted-by: Codex GPT-5; reviewed by @zhangxinyao88 before posting

[boring-cyborg]

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