Flake: test_estimate_parallel_readout_errors_batching

[balopat]

Description of the issue

https://github.com/quantumlib/Cirq/pull/4334/checks?check_run_id=3300474396

________________ test_estimate_parallel_readout_errors_batching ________________

    def test_estimate_parallel_readout_errors_batching():
        qubits = cirq.LineQubit.range(10)
        sampler = cirq.ZerosSampler()
Coverage.py warning: Data file '/home/runner/work/Cirq/Cirq/.coverage.fv-az204-721.2736.855433' doesn't seem to be a coverage data file: Couldn't use data file '/home/runner/work/Cirq/Cirq/.coverage.fv-az204-721.2736.855433': no such table: coverage_schema
        repetitions = 1000
        result = cirq.estimate_parallel_single_qubit_readout_errors(
            sampler, qubits=qubits, repetitions=repetitions, trials=45, trials_per_batch=10
        )
>       assert result.zero_state_errors == {q: 0.0 for q in qubits}
E       assert {cirq.LineQub...(3): 0.0, ...} == {cirq.LineQub...(3): 0.0, ...}
E         Omitting 9 identical items, use -vv to show
E         Differing items:
E         {cirq.LineQubit(8): nan} != {cirq.LineQubit(8): 0.0}
E         Full diff:
E           {
E            cirq.LineQubit(0): 0.0,
E            cirq.LineQubit(1): 0.0,
E            cirq.LineQubit(2): 0.0,
E            cirq.LineQubit(3): 0.0,
E            cirq.LineQubit(4): 0.0,
E            cirq.LineQubit(5): 0.0,
E            cirq.LineQubit(6): 0.0,
E            cirq.LineQubit(7): 0.0,
E         -  cirq.LineQubit(8): 0.0,
E         ?                     ^^^
E         +  cirq.LineQubit(8): nan,
E         ?                     ^^^
E            cirq.LineQubit(9): 0.0,
E           }

cirq-core/cirq/experiments/single_qubit_readout_calibration_test.py:182: AssertionError

Cirq version

0.12.0.dev