pyproject.toml: Set disallow_untyped_calls = true (MR 2514)

We pass this check now, might as well.

pyproject.toml

@@ -53,5 +53,6 @@ addopts = [
 [tool.mypy]
 check_untyped_defs = true
 disallow_incomplete_defs = true
+disallow_untyped_calls = true
 disallow_untyped_decorators = true
 disallow_untyped_defs = true