Add Kubernetes provider utility test coverage

[YusefSyed]

Closes #72265.

Why

The Kubernetes task source-rewrite and YAML deletion utilities had no direct
tests. A regression could silently corrupt generated task code, select the wrong
Kubernetes API method, or change deletion error handling without the
project-structure gate noticing the behavior change.

What changed

• Cover task decorators with no arguments, arguments, nested parentheses, setup
  and teardown decorators, and absent task decorators.
• Cover script rendering, native Jinja rendering, and strict missing-context
  behavior.
• Cover Kubernetes API class derivation for core, named, .k8s.io, and
  multi-label DNS groups.
• Cover CamelCase method conversion, namespaced and cluster-scoped dispatch,
  namespace precedence, List expansion, inherited API versions, and aggregated
  ApiException formatting.
• Remove the two matching entries from OVERLOOKED_TESTS.

Verification

• Direct combined provider tests: 14 passed.
• airflow-core/tests/unit/always/test_project_structure.py: 10 passed, 1
  expected xfail.
• Applicable Ruff, mypy, license, test-location, and pre-commit checks: passed.
• The two requested Breeze commands were attempted, but the local Docker
  CI-image build ended before producing a test result. No Breeze success is
  claimed. Hosted CI is the remaining environment-level verification.

Generative AI tools assisted with repository navigation, test drafting, command
execution, and diff analysis. The resulting three-file test-only change was
narrowed to direct utility coverage and removal of the two matching
overlooked-test entries, then verified with the checks listed above.

The account holder reviewed and approved the final three-file diff and
validation evidence on 2026-09-04 and accepts final responsibility for the
contribution.

---

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

• Yes - OpenAI Codex (GPT-5.6 Sol)

Generated-by: OpenAI Codex (GPT-5.6 Sol) following the
guidelines

[boring-cyborg]

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