Fix schema generation error when serialization schema holds references

[Viicos]

Change Summary

Fixes #10443.
I'm not too happy with the solution, feels a bit weird to have to worry about this inside count_refs, but couldn't find a better fix.

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 #10444 will improve performances by 13.81%

_{Comparing 10443 (6f29c68) with main (01daafa)}

Summary

⚡ 1 improvements
✅ 36 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	10443	Change
⚡	test_field_validators_serializers	2.8 ms	2.5 ms	+13.81%

[github-actions]

Coverage report

Click to see where and how coverage changed

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

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

[sydney-runkle]

Seems alright to me for now, thanks for adding the inline comment.