Update mypy-dev to 1.12.0a3

[cdce8p]

Proposed change

https://github.com/cdce8p/mypy-dev/releases/tag/1.12.0a3
Compare: python/mypy@e67decb...0a6d40b

• Bug fixes
• Updated typeshed stubs

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

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