Bump pytest-asyncio from 0.20.3 to 0.21.0 (#354)

Bumps [pytest-asyncio](https://github.com/pytest-dev/pytest-asyncio) from 0.20.3 to 0.21.0.
- [Release notes](https://github.com/pytest-dev/pytest-asyncio/releases)
- [Commits](pytest-dev/pytest-asyncio@v0.20.3...v0.21.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Sam Bull <aa6bs0@sambull.org>

Author: dependabot[bot]

requirements.txt

@@ -4,6 +4,6 @@ docutils==0.19
 mypy==1.2.0; implementation_name=="cpython"
 pre-commit==2.21.0
 pytest==7.3.1
-pytest-asyncio==0.20.3
+pytest-asyncio==0.21.0
 pytest-cov==4.0.0
 twine==4.0.2