CI: Run mypy with --disallow-untyped-calls

This way we're even stricter with missing types. Let's activate it so we
don't regress.

.ci/mypy.sh

@@ -10,4 +10,4 @@ fi
 
 set -x
 
-mypy mrhlpr.py mrtest.py --check-untyped-defs
+mypy mrhlpr.py mrtest.py --check-untyped-defs --disallow-untyped-calls
\ No newline at end of file