Bump attrs from 21.2.0 to 21.4.0
Bump attrs from 21.2.0 to 21.4.0

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] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
burningmantech/ranger-ims-server,burningmantech/ranger-ims-server,burningmantech/ranger-ims-server,burningmantech/ranger-ims-server