Update mkdocstrings[python] requirement from ==0.26.* to ==0.27.* (#515)

* Update mkdocstrings[python] requirement from ==0.26.* to ==0.27.*

Updates the requirements on [mkdocstrings[python]](https://github.com/mkdocstrings/mkdocstrings) to permit the latest version.
- [Release notes](https://github.com/mkdocstrings/mkdocstrings/releases)
- [Changelog](https://github.com/mkdocstrings/mkdocstrings/blob/main/CHANGELOG.md)
- [Commits](mkdocstrings/mkdocstrings@0.26.0...0.27.0)

---
updated-dependencies:
- dependency-name: mkdocstrings[python]
  dependency-type: direct:development
...

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Co-authored-by: Jirka Borovec <6035284+Borda@users.noreply.github.com>

Author: dependabot[bot]

requirements/dev.txt

@@ -3,7 +3,8 @@ bump2version ==1.0.1
 # coverage >=4.5.4
 mkdocs-material ==9.5.*
 ipython[notebook] >8.0, <9.0
-mkdocstrings[python] ==0.26.*
+mkdocstrings[python] ==0.26.*; python_version < "3.9"
+mkdocstrings[python] ==0.27.*; python_version >= "3.9"
 mknotebooks ==0.8.*
 pytest >=5.3.2
 pytest-runner >=5.1