Bump attrs from 21.3.0 to 21.4.0 (#1198)

Bumps [attrs](https://github.com/python-attrs/attrs) from 21.3.0 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](python-attrs/attrs@21.3.0...21.4.0)

---
updated-dependencies:
- dependency-name: attrs
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

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

Author: dependabot[bot]

poetry.lock

@@ -62,7 +62,7 @@ typing-extensions = ">=4.0,<5.0"
 anyio = "^3.4"
 curio = "^1.5"
 trio = "^0.19"
-attrs = "^21.3"
+attrs = "^21.4"
 httpx = "^0.21"
 
 mypy = "^0.930"