[BUG] Intermittent test failure: `test_ivf_flat.py::test_filtered_ivf_flat[0.5]`

This is to track an intermittent test failure seen in CI. For instance, the CI run for #1366:

=================================== FAILURES ===================================
_________________________ test_filtered_ivf_flat[0.5] __________________________

sparsity = 0.5

    @pytest.mark.parametrize("sparsity", [0.5, 0.7, 1.0])
    def test_filtered_ivf_flat(sparsity):
>       run_filtered_search_test(ivf_flat, sparsity)

python/cuvs/cuvs/tests/test_ivf_flat.py:155: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

search_module = <module 'cuvs.neighbors.ivf_flat' from '/pyenv/versions/3.10.18/lib/python3.10/site-packages/cuvs/neighbors/ivf_flat/__init__.py'>
sparsity = 0.5, n_rows = 10000, n_cols = 10, n_queries = 10, k = 10
...
...
>       assert recall > 0.7
E       AssertionError

/pyenv/versions/3.10.18/lib/python3.10/site-packages/cuvs/tests/ann_utils.py:125: AssertionError
=========================== short test summary info ============================
FAILED python/cuvs/cuvs/tests/test_ivf_flat.py::test_filtered_ivf_flat[0.5] - AssertionError
===== 1 failed, 16008 passed, 149 skipped, 2 xfailed in 574.57s (0:09:34) ======

Apologies if this is being tracked elsewhere already.

Start with python/cuvs/cuvs/tests/test_ivf_flat.py, especially test_filtered_ivf_flat and its call to run_filtered_search_test. Reproduce the failure using the reported CI test and inspect the recall assertion in ann_utils.py:125. Done means identifying why the intermittent recall falls below 0.7 and making the test reliably pass without weakening its intended check.