Merge unit-tests job, and use post-build-check as input for its job

[cecemei]

Status: fkirc/skip-duplicate-actions looks interesting, but this PR is not being worked actively.

Merge unit-tests-unapproved & unit-tests-approved jobs to a single one, and refactor to use post-build-check job to decide whether to run ITS after build ✅ or after unit test ✅.

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This PR has:

• [x] been self-reviewed.
  • [ ] using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• [ ] added documentation for new or modified features or behaviors.
• [ ] a release note entry in the PR description.
• [ ] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• [ ] added or updated version, license, or notice information in licenses.yaml
• [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• [ ] added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• [ ] added integration tests.
• [ ] been tested in a test Druid cluster.