Bump iminuit from 2.25.2 to 2.26.0

Bumps [iminuit](https://github.com/scikit-hep/iminuit) from 2.25.2 to 2.26.0.
- [Release notes](https://github.com/scikit-hep/iminuit/releases)
- [Changelog](https://github.com/scikit-hep/iminuit/blob/develop/doc/changelog.rst)
- [Commits](scikit-hep/iminuit@v2.25.2...v2.26.0)

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

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