chore(deps): update mypy requirement from ==2.1.* to ==2.3.* (#273)

Updates the requirements on [mypy](https://github.com/python/mypy) to permit the latest version.
- [Changelog](https://github.com/python/mypy/blob/master/CHANGELOG.md)
- [Commits](python/mypy@v2.1.0...v2.3.0)

---
updated-dependencies:
- dependency-name: mypy
  dependency-version: 2.3.0
  dependency-type: direct:production
...

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Author: dependabot[bot]

requirements-testing.txt

@@ -8,7 +8,7 @@ pytest-xdist == 3.8.*
 black == 26.*; python_version >= '3.10'
 black == 25.*; python_version < '3.10'
 ruff == 0.15.*
-mypy == 2.1.*; python_version >= '3.10'
+mypy == 2.3.*; python_version >= '3.10'
 mypy == 1.19.*; python_version < '3.10'
 psutil == 7.2.*
 types-PyYAML ~= 6.0