Update pytest-asyncio requirement from ^0.18 to ^0.20 (#8)

Updates the requirements on [pytest-asyncio](https://github.com/pytest-dev/pytest-asyncio) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest-asyncio/releases)
- [Changelog](https://github.com/pytest-dev/pytest-asyncio/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-asyncio@v0.18.0...v0.20.3)

---
updated-dependencies:
- dependency-name: pytest-asyncio
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pyproject.toml

@@ -24,7 +24,7 @@ black = "^22.3.0"
 isort = "^5.10.1"
 poethepoet = "^0.16.5"
 pytest = "^7.1.2"
-pytest-asyncio = "^0.18"
+pytest-asyncio = "^0.20"
 flake8 = "^6.0.0"
 pylint = "^2.14.5"