Bug 1771235 [wpt PR 34209] - Bump mypy from 0.950 to 0.960 in /tools, a=testonly

Automatic update from web-platform-tests
Bump mypy from 0.950 to 0.960 in /tools

Bumps [mypy](https://github.com/python/mypy) from 0.950 to 0.960.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](https://github.com/python/mypy/compare/v0.950...v0.960

)

---
updated-dependencies:
- dependency-name: mypy
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
--

wpt-commits: b293894e545af62931b996700bcfe06b5786414b
wpt-pr: 34209