fix: correct the positional encoding of Transformer in pytorch examples

[Galaxy-Husky]

What does this PR do?

Fixes #19138

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📚 Documentation preview 📚: https://pytorch-lightning--20203.org.readthedocs.build/en/20203/

[iamrishiksahu]

Hi @Jay-Karia, I would like to work on this enhancement. Kindl assign it to me.

[Jay-Karia]

@iamrishiksahu, there is no need to assign issues, you can just send a pull !