logictest: create linter to prevent checking in underscore-prefixed test files

[mgartner]

As of #85386, logic test files that start with an underscore are considered "temporary" files that run in the TestLogic_tmp test. They are meant for local development and debugging, and they shouldn't be checked in to the repository. We should create a linter to enforce this. See the discussion: #85386 (review)

Jira issue: CRDB-18254

[github-actions]

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