build(deps): bump pytest-doctestplus from 1.5.0 to 1.6.0 in /requirements (#21373)

build(deps): bump pytest-doctestplus in /requirements

Bumps [pytest-doctestplus](https://github.com/scientific-python/pytest-doctestplus) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/scientific-python/pytest-doctestplus/releases)
- [Changelog](https://github.com/scientific-python/pytest-doctestplus/blob/main/CHANGES.rst)
- [Commits](https://github.com/scientific-python/pytest-doctestplus/compare/v1.5.0...v1.6.0)

---
updated-dependencies:
- dependency-name: pytest-doctestplus
  dependency-version: 1.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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