CommandGraph/Scheduler tests sporadically hanging on Win

Example:
https://github.com/intel/llvm/actions/runs/28109685318/job/83233372356
https://github.com/intel/llvm/actions/runs/28128053215/job/83296892430

Start with the two linked GitHub Actions jobs and inspect the CommandGraph/Scheduler tests that hang on Windows. Reproduce the sporadic hang in that environment, then verify that the affected tests complete reliably without hangs.

Written by the indexing model from the issue text.