Build(deps-dev): Bump xdoctest from 0.15.5 to 0.15.6

Bumps [xdoctest](https://github.com/Erotemic/xdoctest) from 0.15.5 to 0.15.6.
- [Release notes](https://github.com/Erotemic/xdoctest/releases)
- [Changelog](https://github.com/Erotemic/xdoctest/blob/master/CHANGELOG.md)
- [Commits](Erotemic/xdoctest@0.15.5...0.15.6)

---
updated-dependencies:
- dependency-name: xdoctest
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

pyproject.toml

@@ -31,7 +31,7 @@ coverage = {extras = ["toml"], version = "^5.5"}
 safety = "^1.10.3"
 mypy = "^0.910"
 typeguard = "^2.12.1"
-xdoctest = {extras = ["colors"], version = "^0.15.5"}
+xdoctest = {extras = ["colors"], version = "^0.15.6"}
 sphinx = "^4.1.2"
 sphinx-autobuild = "^2021.3.14"
 pre-commit = "^2.13.0"