Bump attrs from 21.2.0 to 21.4.0 (#3386)

Bumps [attrs](https://github.com/python-attrs/attrs) from 21.2.0 to 21.4.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/python-attrs/attrs/compare/21.2.0...21.4.0)

---
updated-dependencies:
- dependency-name: attrs
  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>

requirements.txt

@@ -1,7 +1,7 @@
 aiohttp==3.8.1
 async_timeout==4.0.2
 atomicwrites==1.4.0
-attrs==21.2.0
+attrs==21.4.0
 awesomeversion==22.1.0
 brotli==1.0.9
 cchardet==2.1.7