Always store the original field assignment on FieldInfo

[Viicos]

Change Summary

Fixes #11920.

Related issue number

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[cloudflare-workers-and-pages]

Deploying pydantic-docs with    Cloudflare Pages

Latest commit:	b0785ec
Status:	✅  Deploy successful!
Preview URL:	https://51b2392f.pydantic-docs.pages.dev
Branch Preview URL:	https://store-original-assignment.pydantic-docs.pages.dev

View logs

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
pydantic/_internal
_fields.py
Project Total

This report was generated by python-coverage-comment-action

[codspeed-hq]

CodSpeed Performance Report

Merging #11946 will not alter performance

_{Comparing store-original-assignment (b0785ec) with main (88c75cd)}

Summary

✅ 46 untouched benchmarks