XGBoost hyperparameters string values incorrectly json-dumped with extra quotes causing validation to fail

[zachliu]

Describe the bug
The hyperparameters in XGBoost are incorrectly json-dumped with extra quotes which causes the validation to fail.

To reproduce

sample code

from sagemaker.xgboost.estimator import XGBoost

params = {
    "objective": "reg:squarederror",
    "num_round": 100,
    "max_depth": 5,
    "eta": 0.1,
    "subsample": 0.8,
}

xgb = XGBoost(
    entry_point=None,  # using built-in algorithm mode
    hyperparameters=params,
    framework_version="1.7-1",
    instance_type="ml.m5.xlarge",
    instance_count=1,
    role=role,
    output_path=f"s3://{bucket}/{prefix}/output",
)

print(xgb._hyperparameters)
print(xgb.hyperparameters())

will print out

{'objective': 'reg:squarederror', 'num_round': 100, 'max_depth': 5, 'eta': 0.1, 'subsample': 0.8}
{'objective': '"reg:squarederror"', 'num_round': '100', 'max_depth': '5', 'eta': '0.1', 'subsample': '0.8'}

Later at the xbg.fit stage, the training failure:

sagemaker_algorithm_toolkit.exceptions.UserError: Hyperparameter objective: "reg:squarederror" is not in ['aft_loss_distribution', 'binary:logistic', 'binary:logitraw', 'binary:hinge', 'count:poisson', 'multi:softmax', 'multi:softprob', 'rank:pairwise', 'rank:ndcg', 'rank:map', 'reg:linear', 'reg:squarederror', 'reg:logistic', 'reg:gamma', 'reg:pseudohubererror', 'reg:squaredlogerror', 'reg:absoluteerror', 'reg:tweedie', 'survival:aft', 'survival:cox']

Expected behavior
xgb.hyperparameters() should not produce the extra-double-quoted '"reg:squarederror"'. Instead, it should be just 'reg:squarederror'

Screenshots or logs
N/A

System information
A description of your system. Please provide:

• SageMaker Python SDK version: 2.252.0
• Framework name (eg. PyTorch) or algorithm (eg. KMeans): XGBoost
• Framework version: sagemaker-xgboost:1.7-1