test: unskip unfinished update handler cases on time-skipping server

[Sakshamm-Goyal]

Summary

• unskip the unfinished-handler matrix for the time-skipping environment
• accept the documented NOT_FOUND update-poll outcome when a continue-as-new interrupts an unfinished update handler
• preserve the existing WorkflowUpdateFailedError assertion for servers that report the aborted update as an outcome

The workflow runtime warning already documents that interrupted update handlers can cause clients to receive workflow execution already completed; the time-skipping server exposes that path directly.

Validation

• pytest tests/worker/test_workflow.py::test_unfinished_handler_on_workflow_termination -q --workflow-environment time-skipping (48 passed)
• pytest tests/worker/test_workflow.py::test_unfinished_handler_on_workflow_termination -q (48 passed)
• ruff format --check tests/worker/test_workflow.py
• python -m compileall -q tests/worker/test_workflow.py

Closes #826.

[Sakshamm-Goyal]

CI exposed one additional static check after unskipping this parametrized test: its env fixture was no longer used, so BasedPyright treated it as a warning and the lint sequence failed. I removed only that unused parameter in 9629fc9. The complete 48-case time-skipping matrix, Ruff formatting, Mypy, and BasedPyright all pass locally; CI is rerunning on the repaired head.