🌐 [i18n-KO] Fixed tutorial/preprocessing.mdx

[sim-so]

What does this PR do?

Fixed some words and expressions to align with the latest translation works.
This PR is a revision to apply key terms and phrases that have been established over the course of translating several documents.

Here are the main changes:

• dataset : 데이터셋 -> 데이터 세트
• truncation : 생략 -> 잘라내기
• train : 학습 -> 훈련

Some other sentences have also been modified to read more naturally.

Thank you in advance for your review!

Fixes #22578
Part of #20179

Before reviewing

• Check for missing / redundant translations (번역 누락/중복 검사)
• Grammar Check (맞춤법 검사)
• Review or Add new terms to glossary (용어 확인 및 추가)
• Check Inline TOC (e.g. [[lowercased-header]])
• Check live-preview for gotchas (live-preview로 정상작동 확인)

Who can review? (Initial)

Team PseudoLab, may you please review this PR?
@0525hhgus, @kihoon71, @sim-so, @gabrielwithappy, @HanNayeoniee, @wonhyeongseo, @jungnerd

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

May you please review this PR?
@sgugger, @ArthurZucker, @eunseojo

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[wonhyeongseo]

LGTM 💯 I especially liked how you used colloquial terms, making the documentation more readable. Thank you for your revision!

[ArthurZucker]

Thanks for the changes! 🤗

[amyeroberts]

Thanks for updating!