Bump graphviz from 0.20.1 to 0.20.2 (#6)

Bumps [graphviz](https://github.com/xflr6/graphviz) from 0.20.1 to 0.20.2.
- [Changelog](https://github.com/xflr6/graphviz/blob/master/CHANGES.rst)
- [Commits](xflr6/graphviz@0.20.1...0.20.2)

---
updated-dependencies:
- dependency-name: graphviz
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

requirements/test.txt

@@ -5,7 +5,7 @@ pytest-cov ==4.1.0
 pytest-xdist ==3.5.0
 pytest-random-order ==1.1.1
 pytest-timestamper ==0.0.9
-graphviz ==0.20.1
+graphviz ==0.20.2
 fdm ==0.4.1
 expecttest ==0.2.1  # for test_ddp.py
 hypothesis ==6.99.8  # for test_ddp.py