[Bugfix][CI] Fix test_remote_decode_lifecycle.py::test_short_prompt_lifecycle

[NickLucche]

This test is failing on main, preventing clean merges. With this PR it fails no more

(llmd) ➜  vllm git:(78077d541) ✗ glog | head -n 1                                                                                         
* 78077d541 (HEAD, upstream/main) Move `SchedulerConfig` from `config/__init__.py` to `config/scheduler.py` (#22626)
(llmd) ➜  vllm git:(78077d541) ✗ p -m pytest -q --tb=no tests/v1/kv_connector/unit/test_remote_decode_lifecycle.py::test_short_prompt_lifecycle 

F                                                                                                                                                              [100%]
====================================================================== short test summary info =======================================================================
FAILED tests/v1/kv_connector/unit/test_remote_decode_lifecycle.py::test_short_prompt_lifecycle - AssertionError
1 failed in 10.59s
(llmd) ➜  vllm git:(78077d541) ✗ 
(llmd) ➜  vllm git:(78077d541) ✗ gsw pd-fix-test 
Previous HEAD position was 78077d541 Move `SchedulerConfig` from `config/__init__.py` to `config/scheduler.py` (#22626)
Switched to branch 'pd-fix-test'
(llmd) ➜  vllm git:(pd-fix-test) ✗ p -m pytest -q --tb=no       tests/v1/kv_connector/unit/test_remote_decode_lifecycle.py::test_short_prompt_lifecycle
.                                                                                                                                                              [100%]
1 passed in 10.94s

Test introduced in #21074.

[gemini-code-assist]

Code Review

This pull request addresses a bug in test_short_prompt_lifecycle where the test was failing due to an incorrect assignment. The original code attempted to set a finished_sending attribute on a ModelRunnerOutput instance, which does not have this attribute, leading to test failure and potential memory leaks.

The fix correctly replaces this with a call to the create_model_runner_output utility function. This function properly constructs a ModelRunnerOutput object, including the nested KVConnectorOutput with the finished_sending information. This ensures that the scheduler is correctly notified about the finished KV transfer, allowing it to free the associated resources.

The change is clean, effective, and resolves the bug. The test now passes as expected.

[github-actions]

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[DarkLight1337]

Seems we have another test failure related to Gemma3n, let's fix that in the next PR 😅