Ignore missing mypy imports

Author: dstansby

pyproject.toml

@@ -51,6 +51,7 @@ disallow_incomplete_defs = true
 disallow_untyped_defs = true
 no_implicit_reexport = true
 warn_return_any = false # TODO: fix
+ignore_missing_imports = true
 
 [[tool.mypy.overrides]]
 module = [