Partially Use f string (#10218)

* flynt. trial 1.

* Trial 1.

* Addressed code review.

python/ray/prometheus_exporter.py

@@ -217,8 +217,7 @@ class Collector(object):
             return metric
 
         else:
-            raise ValueError(
-                "unsupported aggregation type %s" % type(agg_data))
+            raise ValueError(f"unsupported aggregation type {type(agg_data)}")
 
     def collect(self):  # pragma: NO COVER
         """Collect fetches the statistics from OpenCensus