Bump attrs from 20.3.0 to 21.2.0

Bumps [attrs](https://github.com/python-attrs/attrs) from 20.3.0 to 21.2.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/main/CHANGELOG.rst)
- [Commits](python-attrs/attrs@20.3.0...21.2.0)

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

Author: dependabot[bot]

test-requirements.txt

@@ -8,7 +8,7 @@ alabaster==0.7.12
     # via sphinx
 async-generator==1.10
     # via -r test-requirements.in
-attrs==20.3.0
+attrs==21.2.0
     # via pytest
 babel==2.9.0
     # via sphinx