```constraint``` and ```allow_duplicate_points``` can't be used at the same time.

constraint and allow_duplicate_points can't be used at the same time.

I want to optimize a 4-D function f(x,y,z,k) with constraint z<k and I will get some duplicate points during BO process. So I need to use constraint and allow_duplicate_points at the same time. But it seems that these two functions can't work together although the script runs smoothly when they are used separately.

Here is my code

def constraint_function(x,y,z,k):
    return z-k

constraint_lower = -np.inf
constraint_upper = 0

constraint = NonlinearConstraint(constraint_function, constraint_lower, constraint_upper)

optimizer = BayesianOptimization(
    f=None,
    constraint=constraint,
    pbounds={"x": (2, 2.5),"y":(0.5, 1.0), "z":(11,11.5) , "k":(11,11.5)},
    verbose=0,
    random_state=1,
    allow_duplicate_points=True,
)

utility = UtilityFunction(kind="ei", kappa=10, xi=0)

#iter
optimizer.register(params={'x': 2.500, 'y': 0.600, 'z': 11.000, 'k': 11.500}, target=-2.78000, constraint_value=constraint_function(2.500,0.600,11.000,11.500))
#------------------------------------------------------
optimizer.register(params={'x': 2.216, 'y': 0.653, 'z': 11.178, 'k': 11.192}, target=-26.57100, constraint_value=constraint_function(2.216,0.653,11.178,11.192))
#------------------------------------------------------
optimizer.register(params={'x': 2.411, 'y': 0.916, 'z': 11.138, 'k': 11.437}, target=-100.00000, constraint_value=constraint_function(2.411,0.916,11.138,11.437))
optimizer.register(params={'x': 2.411, 'y': 0.916, 'z': 11.138, 'k': 11.437}, target=-90.00000, constraint_value=constraint_function(2.411,0.916,11.138,11.437))
#------------------------------------------------------

ERROR 316246465-b5b85505-1657-4843-a44a-7750892cdb58

I have used allow_duplicate_points=True, But I sill got this error.

Environment

python Version [3.9 or 3.8]
bayesian-optimization Version [1.4.3]

bayesian-optimization / BayesianOptimization

```constraint``` and ```allow_duplicate_points``` can't be used at the same time. #471