test: add unit test increasing coverage for cleanup.py

[cheesebee123]

Problem:
The close_runners utility function located in google.adk.cli.utils.cleanup lacked dedicated unit test coverage to ensure it properly handles and awaits the asynchronous close method on provided runner instances.

Solution:
Added a new asynchronous unit test (test_close_runners_calls_close) using unittest.mock (Mock and AsyncMock) to verify that when close_runners is called, the close method of each runner in the list is successfully awaited exactly once.

Testing Plan:

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

platform win32 -- Python 3.11.14, pytest-9.0.3, pluggy-1.6.0
rootdir: C:\Users\Dr. Puffyapple\Documents\Google_ADK_Unittests\adk-python
configfile: pyproject.toml
plugins: anyio-4.13.0, langsmith-0.8.4, asyncio-1.3.0, cov-7.1.0, mock-3.15.1, xdist-3.8.0
asyncio: mode=Mode.AUTO, debug=False, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collected 1 item `

tests\unittests\cli\utils\test_cleanup.py . [100%]

============================================================================== 1 passed in 3.37s ==============================================================================

Manual End-to-End (E2E) Tests:

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

Add any other context or screenshots about the feature request here.

[adk-bot]

Response from ADK Triaging Agent

Hello @cheesebee123, thank you for creating this PR!

It looks like the header-check status check has failed because the newly added file tests/unittests/cli/utils/test_cleanup.py is missing the Apache 2.0 license header.

Could you please add the license header to tests/unittests/cli/utils/test_cleanup.py? You can run pre-commit run --all-files (or use Google's addlicense tool) to automatically format and add the license headers.

This information will help reviewers to review your PR more efficiently. Thanks!