Increase num qubit for grover bit ordering unit test

[t-imamichi]

Summary

Follow-up of #97

I notice that a unit test may fail on Linux as follows.

======================================================================
FAIL: test_bit_ordering_1_sv (test.algorithms.test_grover_optimizer.TestGroverOptimizer)
Test bit ordering
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ima/envs/dev/lib/python3.8/site-packages/ddt.py", line 182, in wrapper
    return func(self, *args, **kwargs)
  File "/home/ima/qiskit/opt/test/algorithms/test_grover_optimizer.py", line 236, in test_bit_ordering
    self.assertEqual(results.fval, opt_sol)
AssertionError: 0.0 != -2
----------------------------------------------------------------------

It is required to make #129 pass.

Details and comments

[t-imamichi]

We need more investigation because @manoelmarques runs CI again with #129 and we found that CI succeeds without this PR. It looks strange...
https://github.com/Qiskit/qiskit-optimization/runs/2575783380

[t-imamichi]

I close it because we implemented a better solution #132.