[ModelicaSystem] fix mypy: use self.resultfile

Author: syntron

OMPython/ModelicaSystem.py

@@ -910,7 +910,7 @@ def simulate(self, resultfile: Optional[str] = None, simflags: Optional[str] = N
 
         if self.inputFlag:  # if model has input quantities
             # csvfile is based on name used for result file
-            csvfile = resultfile.parent / f"{resultfile.stem}.csv"
+            csvfile = self.resultfile.parent / f"{self.resultfile.stem}.csv"
 
             for i in self.inputlist:
                 val = self.inputlist[i]