actually use f string

Contributes to CURA-11482

plugins/CuraEngineBackend/StartSliceJob.py

@@ -337,7 +337,7 @@ class StartSliceJob(Job):
 
         user_id = uuid.getnode()  # On all of Cura's supported platforms, this returns the MAC address which is pseudonymical information (!= anonymous).
         user_id %= 2 ** 16  # So to make it anonymous, apply a bitmask selecting only the last 16 bits. This prevents it from being traceable to a specific user but still gives somewhat of an idea of whether it's just the same user hitting the same crash over and over again, or if it's widespread.
-        self._slice_message.sentry_id = "{user_id}"
+        self._slice_message.sentry_id = f"{user_id}"
         self._slice_message.cura_version = CuraVersion
 
         # Build messages for extruder stacks