fix: use validator name instead of tag value in tagged union error loc

[JaeHyuckSa]

Change Summary

Tagged union errors currently show the discriminator’s tag value (e.g., apple, tag_for_a) in loc. This change makes them show the validator name instead (e.g., typed-dict).

Related issue number

fix: pydantic/pydantic#10433

Checklist

• Unit tests for the changes exist
• Documentation reflects the changes where applicable
• Pydantic tests pass with this pydantic-core (except for expected changes)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/validators/union.rs	0.00%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[codspeed-hq]

Merging this PR will not alter performance

✅ 163 untouched benchmarks

---

_{Comparing JaeHyuckSa:fix-issue-10433 (b8d44b0) with main (383eb95)}

[JaeHyuckSa]

This was accidentally opened against the wrong repository. I’ve fixed it and opened a new PR for Pydantic instead.

• fix: use validator name instead of tag in tagged union error location pydantic#12731