Confusing reference to variable in `LOAD DATA` document

[imtbkcat]

Error Report

This repository is ONLY used to solve issues related to DOCS.
For other issues (related to TiDB, PD, etc), please move to other repositories.

Please answer the following questions before submitting your issue. Thanks!

1. What is the URL/path of the document related to this issue?
   https://pingcap.com/docs/stable/sql-statements/sql-statement-load-data/
   this document is different from Chinese document.

Also, is confusing at Note part: pingcap/tidb#17800

2. How would you like to improve it?

[yikeke]

This is because this PR is to be translated: pingcap/docs-cn#3335 @imtbkcat We will assign someone to translate it within this week. Until then, this PR welcomes the community's contribution in translation!