[bugfix] Fix an f-string

Change-Id: Ic9a6b87b713af4c09f4ff14519cc5e917188a673

Author: matejsuchanek

pywikibot/page/_wikibase.py

@@ -1738,7 +1738,7 @@ def fromJSON(cls, site, data: dict[str, Any]) -> Claim:
 
             msg = None
             if not claim_type:
-                msg = '{claim.id} does not exist.'
+                msg = f'{claim.id} does not exist.'
             elif claim.type in cls.types:
                 # The default covers string, url types
                 claim.target = cls.TARGET_CONVERTER.get(