Do not use the previous config from the stack for dataclasses without config

[Viicos]

Change Summary

Also fixed in #10530 but in a separate PR for a cleaner commit history.

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 #10576 will not alter performance

_{Comparing dataclass-config-bug (db5e36c) with main (bb7bd96)}

Summary

✅ 38 untouched benchmarks

[sydney-runkle]

Good find, thanks!

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[sydney-runkle]

Maybe we add a test demonstrating that this is not allowed?

@dataclasses.dataclass
class DC:
    a: ArbitraryType
    b: str

class Model(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)

    dc: DC
    other: str