Bump pytest-asyncio from 0.20.3 to 0.21.0

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>

requirements.txt

@@ -6,7 +6,7 @@ grablib==0.8
 Pygments==2.15.1
 pytest==6.2.5
 pytest-aiohttp==1.0.4
-pytest-asyncio==0.20.3
+pytest-asyncio==0.21.0
 pytest-cov==4.1.0
 pytest-forked==1.6.0
 pytest-mock==3.10.0