fix python 3.10 incompatibility

Author: JFoederer

robotmbt/visualise/models.py

@@ -286,7 +286,7 @@ def export_graph(self, dir: str = '', atest: bool = False) -> str | None:
         return None
 
     @staticmethod
-    def import_graph_from_file(file_path: str) -> TraceInfo:
+    def import_graph_from_file(file_path: str):
         try:
             with open(file_path, "r") as f:
                 traceinfo = jsonpickle.decode(f.read())