Fixing overriding from_pretrained with `truncation_side`.
Author: Narsil
Pull request: yes

# What does this PR do?

Make sure users can override `truncation_side` on load.

Fixes #15440

@sgugger

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Fixes # (issue)


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

Closed in favor of https://github.com/huggingface/transformers/pull/15456