fix(robomp): address PR #4184 review nits

- log the worker thread's exception when a workspace op raises during
  caller cancellation, so a persistently failing setup surfaces instead
  of being buried behind CancelledError.
- raise on a timed-out (124) git symbolic-ref probe in the repo-exists
  path, matching the rev-parse probes, instead of silently accepting the
  caller-supplied branch.
- assert the subprocess timeout is passed in the two _chown_workspace
  test fakes so a refactor cannot silently drop the bound.

Op: correct
Restores: spec:indeterminate-git-probes-raise-not-silently-proceed

python/robomp/src/tasks.py

@@ -54,6 +54,12 @@ async def _run_workspace_op(func: Callable[..., _T], /, **kwargs: object) -> _T:
                 continue
             except BaseException:
                 break
+        if not inner.cancelled() and inner.exception() is not None:
+            log.warning(
+                "workspace op %s raised during caller cancellation",
+                getattr(func, "__name__", func),
+                exc_info=inner.exception(),
+            )
         raise