[ModelicaSystem] fix flake8 error

./OMPython/ModelicaSystem.py:1236:72: E999 SyntaxError: f-string: unmatched '['

Author: syntron

OMPython/ModelicaSystem.py

@@ -1232,7 +1232,7 @@ def linearize(self, lintime: Optional[float] = None, simflags: Optional[str] = N
             self.csvFile = self.createCSVData()
             om_cmd.arg_set(key="csvInput", val=self.csvFile.as_posix())
 
-        om_cmd.arg_set(key="l", val=f"{lintime or self.linearOptions["stopTime"]}")
+        om_cmd.arg_set(key="l", val=str(lintime or self.linearOptions["stopTime"]))
 
         # allow runtime simulation flags from user input
         if simflags is not None: