Fix string interpolation. (#23)

Author: blkt

resources/repositories_service.py

@@ -88,4 +88,4 @@ def repository_list_length_equals(self, length):
 
         """
         if not len(self.results["results"]) == int(length):
-            raise ValueError(f"Results should be {length} items long, was {len(self.results["results"])}")
+            raise ValueError(f"Results should be {length} items long, was {len(self.results['results'])}")