fix(mypy) Downgrade mypy
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 5278bddae8373..d66b6b9f37e18 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -2,7 +2,7 @@ docker>=3.7.0,<3.8.0
 exam>=0.5.1
 freezegun==1.1.0
 honcho>=1.0.0,<1.1.0
-mypy>=0.800
+mypy>=0.800,<0.900
 openapi-core @ https://github.com/getsentry/openapi-core/archive/master.zip#egg=openapi-core
 pytest==6.1.0
 pytest-cov==2.11.1

Apparently mypy 0.900 is not compatible.