Ensure __pydantic_complete__ is set when rebuilding dataclasses

[Viicos]

Change Summary

Fixes #10284.

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

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[codspeed-hq]

CodSpeed Performance Report

Merging #10291 will not alter performance

_{Comparing 10284-dc-complete (414f43f) with main (0a78494)}

Summary

✅ 45 untouched benchmarks

[sydney-runkle]

Great, good work here. Let's wait on merging anything until after the v2.9 release - I can do that later this week.

[github-actions]

Coverage report

Click to see where and how coverage changed

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

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