Update mypy requirement from ^0.960 to ^1.4

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](https://github.com/python/mypy/compare/v0.960...v1.4.1)

---
updated-dependencies:
- dependency-name: mypy
  dependency-type: direct:development
...

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