Fix flaky test (race condition) (#2368)

Zephyr doesn't cancel tasks after a failure, meaning we can still write to the output directory. We're pausing on fix as we roll out Iris.

More context about the root cause in #2344

Author: yonromai

lib/levanter/tests/test_new_cache.py

@@ -229,7 +229,7 @@ class ThrowingProcessor(SimpleProcessor):
         def __call__(self, batch: Sequence[Sequence[int]]):
             raise RuntimeError("exc")
 
-    with tempfile.TemporaryDirectory() as tmpdir:
+    with tempfile.TemporaryDirectory(ignore_cleanup_errors=True) as tmpdir:
         with pytest.raises(RuntimeError):
             build_or_load_cache(tmpdir, SimpleShardSource(), ThrowingProcessor())