[BugFix]: KeyError: 'Adafactor is already registered in optimizer at…

[yeshsurya]

… torch.optim'

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Motivation

For solving bug :

Modification

While optimizers are registered, we force to update the optimizer from transformers library because this was the one used prior to same optimizer was introduced by PyTorch

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
Choice was made to force Adafactor from transformers to be used. Hence changes are backward-compatible.

Use cases (Optional)

NA

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDetection or MMPretrain.
4. The documentation has been modified accordingly, like docstring or example tutorials.

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