chore: fix small typo in the documentation about re-encryption

[fd0r]

Following a discussion at the office with @leventdem we noticed a small typo in the documentation. Indeed even in the case of re-encryption the gateway receives the handle and not the cipher-text.

c.f. https://github.com/zama-ai/fhevm/blob/914699f9695c6f5205ec011be1155189f8abba5b/test/encryptedERC20/EncryptedERC20.ts#L76-L91