Fixed erf_ method in the PyTorch frontend.

[he11owthere]

This method was intended to execute an in-place operation on the erf method, but it lacked a return value.

[github-actions]

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[ivy-leaves]

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[he11owthere]

Please remove "bfloat16" from with_supported_dtypes decorator before running the tests until the issue with ivy.Array.repr method has been fixed as mentioned by Ved in #21447. Thank you! 🙂

[Sam-Armstrong]

@he11owthere these changes look very reasonable to me, thanks for the contribution!

[Sam-Armstrong]

ivy-gardener
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