Bump xdoctest from 0.14.0 to 0.15.0

Bumps [xdoctest](https://github.com/Erotemic/xdoctest) from 0.14.0 to 0.15.0.
- [Release notes](https://github.com/Erotemic/xdoctest/releases)
- [Changelog](https://github.com/Erotemic/xdoctest/blob/master/CHANGELOG.md)
- [Commits](Erotemic/xdoctest@0.14.0...0.15.0)

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

Author: dependabot[bot]

poetry.lock

@@ -30,7 +30,7 @@ coverage = {extras = ["toml"], version = "^5.2"}
 safety = "^1.9.0"
 mypy = "^0.782"
 typeguard = "^2.9.1"
-xdoctest = "^0.14.0"
+xdoctest = "^0.15.0"
 sphinx = "^3.2.1"
 sphinx-autobuild = "^2020.9.1"
 pre-commit = "^2.7.1"