Fix Frontend Failing Test: numpy - tensor.paddle.Tensor.mean

[ZJay07]

PR Description

Error was "ValueError: too many values to unpack (expected 3)" from statistical_dtype_values in the function, solved it with adding * for the unused returns from _statistical_dtype_values in the mean test function

Related Issue

Closes ##28485
Closes ##28523
Closes ##28522
Closes ##28521
Closes ##28520

Checklist

• Did you add a function?
• Did you add the tests?
• Did you run your tests and are your tests passing?
• Did pre-commit not fail on any check?
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[Ishticode]

Thank you very much @ZJay07