Update multidict to 6.7.0

[pyup-bot]

This PR updates multidict from 6.6.4 to 6.7.0.

Changelog

6.7.0

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*(2025-10-05)*


Contributor-facing changes
--------------------------

- Updated tests and added CI for CPython 3.14 -- by :user:`kumaraditya303`.

*Related issues and pull requests on GitHub:*
:issue:`1235`.


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Links

• PyPI: https://pypi.org/project/multidict
• Changelog: https://data.safetycli.com/changelogs/multidict/
• Repo: https://github.com/aio-libs/multidict