Hold back mypy <0.990 for type tests (#246)

Author: antonagestam

setup.cfg

@@ -55,7 +55,7 @@ all =
     phantom-types[pydantic]
     phantom-types[dateutil]
 test =
-    mypy>=0.930
+    mypy>=0.930,<0.990
     pytest
     pytest-mypy-plugins>=1.9.3
     coverage