Use f-string formatting for generating the __qualname__ attribute

Author: egguy

django_prometheus/models.py

@@ -50,5 +50,5 @@ def delete(self, *args, **kwargs):
             model_deletes.labels(model_name).inc()
             return super().delete(*args, **kwargs)
 
-    Mixin.__qualname__ = "ExportModelOperationsMixin('{}')".format(model_name)
+    Mixin.__qualname__ = f"ExportModelOperationsMixin('{model_name}')"
     return Mixin