Bump black from 21.7b0 to 21.12b0 (#1165)

Author: dependabot[bot]

requirements/requirements_dev.txt

@@ -1,7 +1,7 @@
 # https://github.com/HypothesisWorks/hypothesis/issues/2113 
 attrs>=19.2.0
 bandit==1.7.0
-black==21.7b0
+black==21.12b0
 dlint==0.12.0
 flake8==3.9.2
 flake8-bandit==2.1.2