Fix code in threading example

[abbycross]

@LenaPer found that the code example is not working as expected in the https://docs.quantum.ibm.com/run/run-jobs-in-session#run-two-vqe-algorithms-in-a-session-by-using-threading section. @jyu00 has provided updated code:

from concurrent.futures import ThreadPoolExecutor
from qiskit_ibm_runtime import EstimatorV2 as Estimator

def minimize_thread(estimator, method):
    return minimize(cost_func, x0, args=(ansatz, hamiltonian, estimator), method=method)

with Session(backend=backend), ThreadPoolExecutor() as executor:
    estimator1 = Estimator()
    estimator2 = Estimator()

    # Use different tags to differentiate the jobs.
    estimator1.options.environment.job_tags = ["cobyla"]
    estimator2.options.environment.job_tags = ["nelder-mead"]

    # Submit the two workloads.
    cobyla_future = executor.submit(minimize_thread, estimator1, "cobyla")
    nelder_mead_future = executor.submit(minimize_thread, estimator2, "nelder-mead")

    # Get workload results.
    cobyla_result = cobyla_future.result()
    nelder_mead_result = nelder_mead_future.result()